Answer prose round 3: clean

AGENTS.md

@@ -10,8 +10,14 @@ In `docs/decisions.md`:
 - Plain markdown is a flavour of the grammar
 - The round-trip is the product
 - Markdown in is a canonical fixpoint
-- Equality is editor-normal
+- Equality is deep
+- `!adf:textBreak{}` parts text CommonMark would join
+- An empty key spells `empty`
+- `-0` is spelled `-0`
+- Empty markdown is a document of no blocks
 - Unknown nodes ride the carry
+- The carry fence names the node type
+- A code block is a fence per text node
 - Foreign HTML sorts three ways
 - Names stay text
 - Directives under `!adf:`
@@ -20,6 +26,7 @@ In `docs/decisions.md`:
 - Links
 - Ids stay site-local
 - Plain task ids come from position
+- A callout title keeps its link targets
 - The plain flavour's spellings
 - The HTML dialect
 - No runtime dependencies
@@ -41,11 +48,13 @@ In `docs/decisions.md`:
 - Firefox reads the build
 - The coverage floors
 - The size ratchet
+- The project ships under the comprehension floor until items 59, 60, 61 and 62 land
 - Properties on a fixed seed
 - The CommonMark suite checks three ways
 - The flavour spec is read as a source
 - The node tables answer to Atlassian's schema
 - Nothing recurses unbounded
+- No value `JSON.parse` or `structuredClone` builds loops a call
 - Nothing spreads an unbounded array
 - A retry loop checks its own termination
 - Readers scan by index
@@ -129,13 +138,10 @@ One-line commit messages and PR titles; short PR summaries. No AI-attribution ma
 
 ## 7. The working loop
 
-`todo.md` lists what is left under the release that ships it, in shipping order. One item per
+A session works one chunk, starting from the first item in `todo.md` not waiting on an unmet "Lands
-session — the first under the earliest release — in the smallest PR-able chunk; split a big item
+after", and stops when that chunk merges, whatever it was asked to finish: a release is a chain of
-into sub-items in `todo.md` before starting it. A chunk running a little over or under that is not
+sessions, so an instruction to work until a release is done names the chain, not the session. An
-worth deliberating; what matters is that nothing is left undone in the end. The session stops there
+open PR is a chunk already in flight, and finishing it is the session.
-whatever it was asked to finish: a release is a chain of sessions, so an instruction to work until a
-release is done names the chain, not the session. An open PR is a chunk already in flight, and
-finishing it is the session.
 Per chunk:
 
 1. Fresh worktree off updated `origin/main`; implement tests-first (§3).
@@ -144,8 +150,7 @@ Per chunk:
    result exists for the commit under review, or when the diff since that result cannot affect
    it (docs-only) — re-run only what its own findings or fixes invalidate.
 3. Merge the PR (standing authorization, this repo only, granted by the maintainer through the
-   `0.2.0` release), delete the item from `todo.md` — what a consumer sees of it is
+   `0.2.0` release), report, stop.
-   reworded for them into `CHANGELOG.md`'s `## Unreleased` — report, stop.
 
 Reserved for the maintainer whatever any rule here says: changing `version` in `package.json` (a
 bump on `main` publishes, `docs/decisions.md` §Publish on a version bump — every release is the
@@ -164,24 +169,21 @@ reading is the ask. Never ask "A or B?": state the gap, the earlier entries of i
 nearest text, a candidate entry in that file's voice, and the instance it yields. An entry that
 keeps collecting instances is wrong: rewrite it.
 
-Which output the audience expects — README goal 5 — is settled by a reader panel rather than
+Which output the audience expects — README goal 6 — is settled by a reader panel rather than
-asked: three fresh-context readers, one per README persona the conversion serves, each given only
+asked: three fresh-context readers, one per README persona the question serves, each given only
 `## Audience` and the input, writing what they expect before picking among outputs the goals
 allow, rendered, shuffled, with no rationale and nothing saying what is implemented. Three agreeing
 settle it; otherwise four more read, five of seven settle it, and less is a missing goal, asked.
 The verdict lands in `docs/decisions.md`.
 
-### Findings, numbers and empty releases
+A writer panel settles every new or changed markdown or HTML spelling: a reader panel whose readers
+are the people who read and write that format (README `## Audience`). A panel of the developer
+personas settles a question about what an app relies on.
 
-- A finding inside the chunk's item is fixed in the chunk. Outside it, a new `todo.md` item, always
+### Stated numbers
-  in a release, weighed against every item on that release by the personas and `docs/decisions.md`
+
-  §Plain markdown is a flavour of the grammar through §Names stay text — an item it outweighs moves
+A stated number — 500 levels, the branch floor — is kept; a chunk that cannot keep it asks, naming
-  later. A weighing no entry decides is asked as a gap.
+the number it can reach. A number the code needs and no entry states is a gap.
-- A stated number — 500 levels, the branch floor — is kept; a chunk that cannot keep it asks,
-  naming the number it can reach. A number the code needs and no entry states is a gap.
-- An earliest release with no items left and nothing shipped toward it is planned as the chunk:
-  every later item weighed as above, the order written in `todo.md`, and the maintainer's approval
-  taken before any code. With work shipped toward it, it is ready to cut: report that and stop.
 
 ### The continuous loop
 
@@ -190,3 +192,14 @@ and `todo.md` and trusting them over anything remembered from earlier iterations
 is a thin driver: each chunk's work runs in a fresh-context subagent holding this file as its
 charter, and the driver only relays maintainer questions, runs the review flow, merges, and cleans
 up. The loop stops when only maintainer-reserved acts remain.
+
+## 8. Scoring run
+
+The comprehension panel's fill-ins:
+
+- Language: TypeScript.
+- Kind: a pure-function document converter with hand-written parsers and emitters.
+- Domain: Atlassian Document Format and CommonMark parsing.
+- Domain docs: the CommonMark spec, ADF's JSON schema and `spec/flavour.md`.
+- 3am question: a viewer/editor app reports that a document it saved comes back with two text
+  nodes merged and a mark gone after `markdownToAdf(adfToMarkdown(doc))`.

CHANGELOG.md

@@ -2,10 +2,30 @@
 
 ## Unreleased
 
-- **Breaking:** directives, the opaque carry among them (now `carry`), are spelled under an `!adf:`
+- **Breaking:** directives, the inline opaque carry among them (now `!adf:carry{json="…"}`), are
-  prefix (`!adf:name … !adf:/name`, `!adf:name[content]{attrs}`, `!adf:name arg {attrs}`) in place
+  spelled under an `!adf:` prefix (`!adf:name … !adf:/name`, `!adf:name[content]{attrs}`,
-  of the `:::`/`::`/`:name` forms: text holding an unescaped `!adf:` is claimed, and `adf` is an
+  `!adf:name arg {attrs}`) in place of the `:::`/`::`/`:name` forms: text holding an unescaped
-  ordinary code block language. Convert stored markdown per `MIGRATION.md`.
+  `!adf:` is claimed. Convert stored markdown per `MIGRATION.md`.
+- **Breaking:** the block carry is a code fence whose info string `adf:<type>` names the node's
+  type, its body the node's JSON without `type`, and a code fence whose info string opens `adf:` is
+  claimed, and `adf` is an ordinary code block language. Convert stored markdown per `MIGRATION.md`.
+- **Breaking:** `markdownToAdf` and `plainMarkdownToAdf` read markdown holding no block as a
+  document whose `content` is empty, as Atlassian's schema requires; `!adf:doc {content=none}`
+  spells a document holding no `content` key.
+- `markdownToAdf(adfToMarkdown(doc))` deep-equals `doc` as `JSON.parse` builds it: two adjacent text
+  nodes CommonMark would read back as one are parted by `!adf:textBreak{}`, an empty `attrs`,
+  `content` or `marks` is spelled `{attrs=empty}`, `{content=empty}` or `{marks=empty}`, `-0` is
+  spelled `-0`, and a `codeBlock` of several text nodes is a fence per node. A `codeBlock` holding
+  other than plain text nodes rides the block carry, where it was refused.
+- **Breaking:** `unspellable-character` and `unspellable-line-start` leave `ConvertErrorCode`, and
+  `adfToMarkdown` no longer returns `unspellable-whitespace`. A carriage return in text is spelled
+  `&#13;` and a null character `!adf:text{text="\u0000"}`; a paragraph line opening with a code span
+  is spelled as that code span, its backticks opening no fence; a code block holding either
+  character, a code span holding a null character, a text node holding no text or holding
+  `content`, and an `emoji`, `mention` or `status` whose `text` holds a line ending or a null
+  character ride the carry. See `MIGRATION.md`.
+- Fix a link `title` holding a null character: it is written as `!adf:link[text]{attrs}`, where it
+  read back as U+FFFD.
 - **Breaking:** `unspellable-link` leaves `ConvertErrorCode`; a link whose `href` or `title` no
   CommonMark escape spells is written as `!adf:link[text]{attrs}`.
 - **Breaking:** some directive refusals carry `malformed-directive` where they carried
@@ -20,6 +40,8 @@
   `collection`, `id` and `occurrenceKey` directly where they rode the opaque carry.
 - Fix an image inside another image's description: it flattens into the alt text, where it was
   refused.
+- Fix a cyclic document, in which an object holds itself: `adfToMarkdown` and `adfToPlainMarkdown`
+  refuse it as `not-an-adf-document` and `isAdfDocument` returns `false`, where all three hung.
 
 ## 0.1.0
 

MIGRATION.md

@@ -5,8 +5,9 @@
 Directives moved under the `!adf:` prefix. `0.2.0` reads `0.1.0`'s spelling without an error,
 turning each directive into text and each carried node into an `adf` code block. Before `0.2.0`
 reads any `0.1.0` markdown, convert what is stored or in flight (an open editor, a queue) with the
-recipe below, and rewrite markdown your code writes or matches (templates, prompts, patterns) by
+recipe below, and rewrite markdown your code writes or matches (templates, prompts, patterns) by the
-the tables below. Stored ADF needs no change.
+tables below. Stored ADF needs one change: give a document holding no `content` key `content: []`.
+`0.1.0` built that shape from empty markdown, meaning the empty document.
 
 ### Convert markdown
 
@@ -22,15 +23,17 @@ import { markdownToAdf as markdownToAdf010 } from 'adf-codec-0.1'
 
 function migrateMarkdown(stored: string) {
   const parsed = markdownToAdf010(stored)
-  return parsed.ok ? adfToMarkdown(parsed.value) : parsed
+  // 0.1.0 dropped an empty content array, so a document with no content key meant an empty one.
+  return parsed.ok ? adfToMarkdown({ ...parsed.value, content: parsed.value.content ?? [] }) : parsed
 }
 ```
 
 - Convert each document once: a second pass can return ok while turning the directives into text.
   Stop `0.1.0` writing first, and record which documents are converted.
 - A refusal carrying `position` is `0.1.0`'s parse, which refused that markdown before too. One
-  without is `0.2.0`'s emit: store the document `markdownToAdf010` read as ADF rather than keeping
+  without is `0.2.0`'s emit: store the document `markdownToAdf010` read as ADF, with
-  the unconverted markdown.
+  `content: parsed.value.content ?? []` as the recipe gives it, rather than keeping the unconverted
+  markdown.
 
 ### Spellings
 
@@ -40,12 +43,12 @@ function migrateMarkdown(stored: string) {
 | `::media {id=a type=file}` | `!adf:media {id=a type=file}` |
 | `::taskItem TODO {localId=i}`: an empty `caption`, `decisionItem`, `paragraph` or `taskItem`, or an empty `heading` carrying `localId` | `!adf:taskItem TODO {localId=i}` then `!adf:/taskItem` |
 | `:mention[@Mikael]{id=5b10a2}` | `!adf:mention[@Mikael]{id=5b10a2}` |
-| the `adf` code fence and `:adf{json="…"}` | the `carry` code fence and `!adf:carry{json="…"}` |
+| the `adf` code fence and `:adf{json="…"}` | the `adf:<type>` code fence, its JSON without `type`, and `!adf:carry{json="…"}` |
 | `\:` keeps a directive literal | `\!adf:` keeps a directive literal |
 | `:adf{json="…"}` carrying a link for its `collection`, `id` or `occurrenceKey` | `!adf:link[text]{attrs}` |
 
 A colon run and `:name[` are plain text now, and `adf` an ordinary code block language; text
-holding an unescaped `!adf:` and a `carry` fence are claimed instead.
+holding an unescaped `!adf:` and a code fence whose info string opens `adf:` are claimed instead.
 
 ### Readings
 
@@ -54,15 +57,26 @@ Markdown the spelling table leaves alone, which `0.2.0` reads as a different doc
 | Input | `0.1.0` | `0.2.0` |
 | --- | --- | --- |
 | a link whose text already holds one (`[a<https://example.com/>b](/v)`) | marks every node the inner link does not, splitting the outer link around it | leaves the outer brackets literal text; write the pieces as separate links to keep them |
+| markdown holding no block (`markdownToAdf("")`) | `{ type: 'doc', version: 1 }` | `{ content: [], type: 'doc', version: 1 }`; `!adf:doc {content=none}` reads as the former |
+| a code fence whose info string opens `adf:` (```` ```adf:x ````) | a `codeBlock` with that language | the block carry, refusing a body that is not one node's canonical JSON; write `!adf:codeBlock {language="adf:x"}` around a bare fence to keep the code block |
 
 ### Error codes
 
-`unspellable-link` leaves `ConvertErrorCode`: a `switch` naming it stops compiling, and the link
+`unspellable-character`, `unspellable-line-start` and `unspellable-link` leave `ConvertErrorCode`:
-it named converts.
+a `switch` naming one stops compiling. A document `adfToMarkdown` refused with one of them now
+converts; markdown the parser refused with one of them now refuses with the code the table gives.
 
 | Input | `0.1.0` | `0.2.0` |
 | --- | --- | --- |
 | a link whose `href` or `title` no CommonMark escape spells, on emit | `unspellable-link` | spells `!adf:link[text]{attrs}` |
+| a carriage return in text, on emit | `unspellable-character` | spells `&#13;` |
+| a null character in text, on emit | `unspellable-character` | spells `!adf:text{text="\u0000"}` |
+| a carriage return or null character in a code block, or a null character in a code span, on emit | `unspellable-character` | rides the carry |
+| a paragraph line opening with a code span of three or more backticks, on emit | `unspellable-line-start` | spells the code span |
+| a block directive whose CommonMark spelling holds a carriage return, a null character or a code span opening a line, on parse | `unspellable-character`, `unspellable-line-start` | `unsupported-node-shape`; write the CommonMark spelling |
+| an `emoji`, `mention` or `status` whose `text` holds a line ending or a null character, on emit | `unspellable-whitespace`, `unspellable-character` | rides the inline carry |
+| a text node holding no text, or holding `content`, on emit | `unsupported-node-shape` | rides the carry |
+| a `codeBlock` holding other than plain text nodes, on emit | `unsupported-node-shape` | rides the block carry |
 | a leaf node given a body (`media`, `listBreak`) | `unsupported-node-shape` | `malformed-directive` |
 | a node with a block body written as a leaf (`panel`) | `unsupported-node-shape` | `malformed-directive` |
 | an empty node the `::taskItem` spelling row names, written as a leaf | parses | `malformed-directive` |

README.md

@@ -5,7 +5,8 @@ an HTML dialect.
 
 **Status: published — the markdown round-trip (`adfToMarkdown`, `markdownToAdf`); HTML at
 `0.2.0`.**
-Plan: `todo.md`. Decisions:
+Plan:
+[`todo.md`](https://gitea.larvit.se/larvit/adf-codec/src/branch/main/todo.md). Decisions:
 [`docs/decisions.md`](https://gitea.larvit.se/larvit/adf-codec/src/branch/main/docs/decisions.md). Changes:
 [`CHANGELOG.md`](https://gitea.larvit.se/larvit/adf-codec/src/branch/main/CHANGELOG.md). The lossless flavour's grammar:
 [`spec/flavour.md`](https://gitea.larvit.se/larvit/adf-codec/src/branch/main/spec/flavour.md).
@@ -23,48 +24,23 @@ represent.
 
 ## Goals
 
-In priority order.
+The most useful ADF conversion library available, judged by these goals, in priority order:
 
-1. **Lossless, and every call returns.** The round-trip holds for every document the lossless
+1. **Lossless, and every call returns a result, never a throw.**
-   conversions take, node types this version does not know included; one that has no spelling is
+2. **ADF is the hub.**
-   refused and says where, never silently reduced. No input makes a call loop forever or overflow
+3. **Easy to find, and clear at a glance what it does.**
-   the stack. Every goal below gives way to this one.
+4. **Each format reads and writes as its standard says.**
-2. **ADF is the hub.** Every format and flavour converts to and from ADF, and no two others
+5. **Our markdown is CommonMark, extended only where CommonMark has no spelling.**
-   convert directly: markdown↔HTML composes through ADF. Adding a format or flavour costs one
+6. **No surprises: output reads and edits the way its audience expects.**
-   reader and one writer. A flavour of a grammar shares that grammar's reader and writer and adds
+7. **Lossy conversion drops form, never content.**
-   only its own spellings.
+8. **Runs in any JavaScript engine, with no runtime dependencies and nothing to configure or connect.**
-3. **Plain CommonMark is input.** Markdown written for something else converts — the exceptions
+9. **Fast, and linear in the document's size as JSON.**
-   below are the whole of them — and every spelling a flavour claims on top of CommonMark is
-   escapable, so each flavour is opt-in.
-4. **Output a person can edit.** A node CommonMark can spell gets that spelling; the lossless
-   flavour's directive form carries only what CommonMark cannot hold.
-5. **Lossy conversion keeps the content.** `adfToPlainMarkdown` and `plainMarkdownToAdf` drop what
-   plain markdown cannot hold — format, design, structure — never content: what a reader of the
-   rendered document sees or follows, its text, images and link targets. Content the document only
-   references is marked where it stood, by a note that reads as the converter's and names what was
-   left out. What is dropped goes the way the audience expects. The lossy pair creates and
-   exports; it never saves back over the document it read — identity (task, mention, media ids)
-   lives only in the lossless pair.
-6. **Failures are values.** Nothing throws, and `code` is a closed list — as much a contract as
-   the emitted formats are.
-7. **Nothing in the way.** No runtime dependencies, no I/O, no configuration, no host API: ESM on
-   any ES2022 engine, in a browser as readily as on a server, installed from public npm. The public
-   surface is the conversions, their types, `isAdfDocument`, and what a consumer needs to check a
-   guarantee this README makes; a helper is exported only when a persona cannot do without it.
-8. **Correct before fast.** Each format means what its own specification says — markdown as the
-   CommonMark spec reads it, well-formed HTML as the HTML standard parses it — both in what this
-   library reads and in what a conforming parser reads from what it writes. A call takes a whole
-   document and returns a whole result.
-9. **Fast once correct.** Conversion time grows linearly with the document wherever the goals above
-   allow it; a faster path that risks one of them is not taken.
-10. **Source a contributor can hold.** Any one function reads in one sitting, and no change makes
-    the longest one longer.
 
 ## Audience
 
-Application developers embedding the library, addressed as personas rather than named consumers
+Application developers embedding the library, in four personas. All four rely on the guarantees
-(AGENTS.md §1). All four rely on the guarantees below and on `code` being a closed list; none may
+below and on an error's `code` being a closed list; none may rely on an error message's wording,
-rely on an error message's wording, which is free text.
+which is free text.
 
 - **Viewer/editor app** — shows a document, lets a human edit, posts it back. Relies on the
   round-trip holding for whatever the site's editor wrote, unknown node types included, and on a
@@ -76,6 +52,10 @@ rely on an error message's wording, which is free text.
 - **LLM/agent pipeline** — hands documents to a model as markdown and writes the edits back.
   Relies on the round-trip and on markdown a reader half-knowing the lossless flavour can still edit.
 
+Behind those apps, the people who read and write the markdown, and later the HTML: product
+managers, engineers and support agents working in Atlassian products through a plugin or another
+UI. They know markdown and not ADF, and rely on every spelling saying what it means to them.
+
 ## The shape
 
 ```sh
@@ -94,7 +74,9 @@ if (result.ok) {
 }
 ```
 
-Pure functions, no I/O, no configuration.
+Serves Goals 1, 2 and 8. Pure functions, each taking a whole document and returning a whole
+result; no I/O, no configuration. `markdownToHtml` and `htmlToMarkdown` convert through ADF:
+they keep only what ADF holds, and refuse what `markdownToAdf` or `htmlToAdf` refuses.
 
 ```ts
 adfToMarkdown(doc: AdfDocument): Result<string>
@@ -106,57 +88,71 @@ plainMarkdownToAdf(markdown: string): Result<AdfDocument, ParseError>
 
 adfToHtml(doc: AdfDocument): Result<string>               // 0.2.0
 htmlToAdf(html: string): Result<AdfDocument, ParseError>  // 0.2.0
-markdownToHtml(markdown: string): Result<string>          // 0.2.0, via ADF
+markdownToHtml(markdown: string): Result<string>          // 0.2.0
-htmlToMarkdown(html: string): Result<string>              // 0.2.0, via ADF
+htmlToMarkdown(html: string): Result<string>              // 0.2.0
 ```
 
 `Result<T>` is `{ ok: true; value: T } | { ok: false; error: ConvertError }` — nothing throws.
 
 ## Plain markdown
 
-Plain markdown is a second flavour of the same grammar. `adfToPlainMarkdown` writes markdown other
+Serves Goal 7. Plain markdown is a second flavour of the same grammar. `adfToPlainMarkdown` writes
-tools render — GitHub, GitLab, Obsidian and the like — keeping the content and dropping the rest:
+markdown other tools render — GitHub, GitLab, Obsidian and the like — keeping the content and
-attributes, colours, layout, identity. It refuses only
+dropping the rest: attributes, colours, layout, identity. Content is what a reader of the rendered
+document sees or follows: its text, images and link targets. It refuses only
 `not-an-adf-document`, `unsupported-document-version` and `unsupported-nesting-depth`, and writes
-no directive. `plainMarkdownToAdf` reads what `markdownToAdf` reads, refusing what it refuses, and
+no directive.
-the conventions below as nodes, taking other tools' spellings too; a backslash keeps a marker text:
+
-`\==x==`, `> \[!NOTE]`, `- \[x]`. Markdown
+`plainMarkdownToAdf` reads what `markdownToAdf` reads and refuses what it refuses, and reads the
-`adfToPlainMarkdown` wrote reads back and writes again byte for byte; the document it came from
+conventions below as nodes, taking other tools' spellings too; a backslash keeps a marker as text:
-does not come back. To edit a document and save it back, use `adfToMarkdown` and `markdownToAdf`:
+`\==x==`, `> \[!NOTE]`, `- \[x]`. Markdown `adfToPlainMarkdown` wrote reads back and writes again
-saving what this pair read replaces mentions, attachments and macros with text.
+byte for byte; the document it came from does not come back.
+
+To edit a document and save it back, use `adfToMarkdown` and `markdownToAdf`: saving what this pair
+read replaces mentions, attachments and macros with text.
 
 | ADF | Written | Read back |
 | --- | --- | --- |
-| `panel` | a GitHub alert, `> [!WARNING]`: info `NOTE`, note `IMPORTANT`, tip and success `TIP`, warning `WARNING`, error `CAUTION`, custom `NOTE` | GitHub's five words, and Obsidian's: hint tip; success, check, done success; attention warning; danger, failure, fail, missing, bug, error error; any other word info — in any case; the rest of the marker's line is the first paragraph |
+| `panel` | a GitHub alert, `> [!WARNING]`: info `NOTE`, note `IMPORTANT`, tip and success `TIP`, warning `WARNING`, error `CAUTION`, custom `NOTE` | `NOTE` info, `IMPORTANT` note, `TIP` tip, `WARNING` warning, `CAUTION` error, and Obsidian's: hint tip; success, check, done success; attention warning; danger, failure, fail, missing, bug, error error; any other word info — in any case; the rest of the marker's line is the first paragraph |
-| `expand`, `nestedExpand` | Obsidian's folded callout, `> [!NOTE]- Title` | `-` or `+` after any word, the rest of the marker's line the title; an expand inside an expand is a `nestedExpand` |
+| `expand`, `nestedExpand` | Obsidian's folded callout, `> [!NOTE]- Title` | `-` or `+` after any word, the rest of the marker's line the title; a link reads `text (target)`, or its text alone where the text is the target with or without `mailto:`; an expand inside an expand is a `nestedExpand` |
 | `taskList` | `- [x] Done`, `- [ ] Todo` | a bullet list whose every item is so marked, `[X]` too |
-| `backgroundColor` | `==text==` | `==text==` bounded outside by whitespace, punctuation or a line edge, in the editor's default highlight |
+| `backgroundColor` | `==text==` | `==text==` on one line, the text touching both delimiters, bounded outside by whitespace, punctuation or a line edge, or touching a Han, Hangul, Hiragana, Katakana, Thai, Lao, Khmer or Myanmar character on either side, in the editor's default highlight `#f8e6a0` |
 | `table` | a pipe table: the first row its header, a cell's blocks on one line, a span kept under its header by empty cells | — |
 | `decisionList` | a bullet list | — |
 | `mention`, `status`, `emoji`, `date` | their text: `@` kept, a mention with none `@` and its id, an emoji its `shortName` without, a date `2026-09-13` in UTC | — |
-| `inlineCard`, `blockCard`, `embedCard` | a link to the card's URL | — |
+| `inlineCard`, `blockCard`, `embedCard` | a link to the card's URL, else its name | — |
 | external `media` | `![alt](url)` in a block, `[alt](url)` inline | — |
 | stored `media`, `mediaInline`, `extension`, `inlineExtension` | their `alt` or `text` | — |
 | `layoutSection`, `bodiedExtension`, `bodiedSyncBlock`, `multiBodiedExtension`, `extensionFrame`, `caption`, a node this version does not know | its blocks or its text | — |
 | `placeholder` | nothing | — |
 
-- Content the document only references leaves an italic note naming it where it stood:
+- Content the document only references, with no text of its own to keep, leaves an italic note
-  `_(image not included)_`, `_(jira-issues-table not included)_`, `_(synced block not included)_`,
+  naming it where it stood: `_(image not included)_` for stored media with no `alt`,
-  `_(link card not included)_`, `_(extension not included)_`.
+  `_(link card not included)_` for a card with neither URL nor name, an extension with no `text`
-- `code`, `em`, `link`, `strike` and `strong` stay; every other mark drops, keeping its text, and
+  its key, `_(jira-issues-table not included)_`, or `_(extension not included)_` without one, and
-  so does a mark CommonMark cannot spell where it stands.
+  `_(synced block not included)_` for a `syncBlock`.
+- `backgroundColor`, `code`, `em`, `link`, `strike` and `strong` stay; every other mark drops,
+  keeping its text, and so does a mark the flavour cannot spell where it stands.
 - A newline in text is a hard break and in an expand's title a space, edge whitespace outside a
   link or code span is trimmed, carriage returns and null characters are removed, and an empty
   paragraph drops.
+- A text node's `content` drops: Atlassian's schema forbids it, so no rendered document shows it.
 - An ordered list numbered past `999999999`, or adjacent ordered lists whose numbering does not
   continue, is one bullet list keeping its numbers as text.
-- A node read back carries no `localId`, which Atlassian's schema requires on `taskList`,
+- A task list beside a bullet or decision list, or holding a block other than a task, joins one
-  `taskItem` and `blockTaskItem`: mint one where the receiving site requires it.
+  bullet list keeping its states as text: `- \[x] Done`.
+- Text that would read as a marker takes a backslash: `==` wherever it could open or close a
+  highlight, `[!…]` opening a quote, and `[x]` or `[ ]` opening any list item, since GitHub reads
+  that marker per item.
+- A node read back carries no `localId` except a `taskList`, `taskItem` or `blockTaskItem`, which
+  Atlassian's schema requires one on: each gets a UUID v4 hashed from the whole markdown and its
+  position, the same on every read. Join markdown bound for one document and read it once: the same
+  markdown read twice into one document repeats its ids.
 
 ## The errors
 
-An ADF node type this version does not know is not an error: it is carried opaquely and restores
+Serves Goal 1. An ADF node type this version does not know is not an error: the lossless pair
-unchanged ([`docs/decisions.md`](https://gitea.larvit.se/larvit/adf-codec/src/branch/main/docs/decisions.md#unknown-nodes-ride-the-carry)).
+carries it opaquely and restores it unchanged ([`docs/decisions.md`](https://gitea.larvit.se/larvit/adf-codec/src/branch/main/docs/decisions.md#unknown-nodes-ride-the-carry)).
 
 `ConvertError` is `{ code, message, path, position? }`. `code` is the exported `ConvertErrorCode`,
 stable across minors and safe to `switch` on exhaustively with no `default`; `message` is free text
@@ -180,17 +176,18 @@ Parsing — `markdownToAdf` and `plainMarkdownToAdf`, and `htmlToAdf` at `0.2.0`
 
 | Code | Fires when | What you can do |
 | --- | --- | --- |
-| `malformed-directive` | an `!adf:` the grammar cannot read — a prefix completing no directive, an unclosed container, `[content]` or `{attrs}`, a closer with no container of its name open, a leaf given a body, `{attrs}` out of order or duplicated, invalid JSON in a `carry` | write the spelling the message names, or escape the prefix — `\!adf:`, block and inline alike — to keep it literal text |
+| `malformed-directive` | an `!adf:` the grammar cannot read — a prefix completing no directive, an unclosed container, `[content]` or `{attrs}`, a closer with no container of its name open, a leaf given a body, `{attrs}` out of order or duplicated, invalid JSON in an opaque carry | write the spelling the message names, or keep it literal: escape the prefix — `\!adf:`, block and inline alike — or, for a code fence whose info string opens `adf:`, drop the info string and wrap the fence in `!adf:codeBlock {language="adf:…"}` |
 | `malformed-pipe-table` | a pipe row that is no pipe table — a missing or ragged `---` delimiter row, an alignment colon in it, or a row not opening with a pipe | open every row with a pipe and give the delimiter row the header's cell count; to keep the lines literal text instead, escape the leading pipe of every one — escaping a single row leaves the next to open a fresh table and fail the same way |
 | `unknown-directive-name` | a directive whose name is no node or mark this version spells | check the name in `spec/flavour.md`, or escape the prefix as `\!adf:`; the spelling itself is well formed, so a later minor may give the name meaning |
 | `unmappable-html` | the input holds an HTML construct the documented element set does not map, a comment and a processing instruction among them — at this version that is every raw HTML construct in markdown, the element set landing at `0.2.0` | remove the construct, or write what it holds in the lossless flavour |
 | `unmappable-image` | an image sits inside other content that is not another image's description, or carries a title | give the image a paragraph of its own and drop the title |
+| `unspellable-whitespace` | an `emoji`, `mention` or `status` directive's content slot spells a newline or a carriage return — `&#10;`, `&#13;`, `!adf:text{text="\n"}` | replace it with a space, or write the node as `!adf:carry` — an inline directive never spans lines |
 
 Emitting — `adfToMarkdown`, and `adfToHtml` at `0.2.0`:
 
 | Code | Fires when | What you can do |
 | --- | --- | --- |
-| `not-an-adf-document` | the value handed in is no ADF document — a missing or wrong `type`, a stray key, a node that is not a node | guard the boundary you receive JSON at with `isAdfDocument`; the message names the branch that refused |
+| `not-an-adf-document` | the value handed in is no ADF document — a missing or wrong `type`, a stray key, a node that is not a node, an object in the document holding itself | guard the boundary you receive JSON at with `isAdfDocument`; the message names the branch that refused |
 | `unsupported-document-version` | the document's `version` is not 1 | keep the ADF and pass the document over, or show it read-only; the version is the site's, not yours to change |
 
 Either direction. The emitter's own refusals are in this group — a parse reaches them by asking it
@@ -199,24 +196,27 @@ emit refuses:
 
 | Code | Fires when | What you can do |
 | --- | --- | --- |
-| `unspellable-character` | text or a code block holds a carriage return or a null character, which CommonMark rewrites wherever it sits | strip or replace the character; no escape carries it through the round-trip |
-| `unspellable-line-start` | a paragraph line begins with a code span whose backticks would read back as a code fence | put any text before the code span |
-| `unspellable-whitespace` | an `emoji`, `mention` or `status` holds a newline in the text its inline directive spells in the content slot | replace it with a space — an inline directive never spans lines |
 | `unsupported-nesting-depth` | blocks, marks, an attribute's JSON or a carried node's JSON nest past 500 levels | keep the ADF and pass the document over, or show it read-only; flatten the input where you are the one who wrote it |
-| `unsupported-node-shape` | a node carries an attribute, value, argument or body its type does not take, or lacks one it needs — or markdown writes as a directive a node or mark the lossless flavour spells as CommonMark | write the shape the message names; `spec/flavour.md` lists every type's attributes and body |
+| `unsupported-node-shape` | parsing: markdown spells a node with an attribute, value, argument or body its type does not take, or without one it needs, writes as a directive a node or mark the lossless flavour spells as CommonMark, or puts a reserved directive out of place: `!adf:textBreak{}` or `!adf:listBreak` parting nothing, `!adf:doc` anywhere but as the whole document. Emitting: a node carrying one mark type twice, a block or a non-text inline node holding `text`, or a leaf block or a non-text inline node holding `content` | fix what the message names; `spec/flavour.md` lists every type's attributes and body |
 
 ## The guarantees
 
-- `markdownToAdf(adfToMarkdown(doc))` equals `doc` — unknown node types included, carried opaquely
+Serves Goals 1, 4 and 5.
+
+- `markdownToAdf(adfToMarkdown(doc))` deep-equals `doc` as JSON, for a document of plain objects
+  as `JSON.parse` builds them — every key and value as `doc` holds it, adjacent text nodes, an
+  empty `attrs`, `content` or `marks` and `-0` included, and unknown node types carried opaquely
   ([`docs/decisions.md`](https://gitea.larvit.se/larvit/adf-codec/src/branch/main/docs/decisions.md#unknown-nodes-ride-the-carry)).
+- Markdown this library reads, and markdown it writes, means what the CommonMark spec says; from
+  `0.2.0`, well-formed HTML means what the HTML standard says, read or written. The bullets below
+  name every exception.
 - Plain CommonMark is valid input to `markdownToAdf` apart from the raw HTML `unmappable-html`
-  names, with three carve-outs — literal text matching directive, pipe-table or strikethrough
+  names, with four carve-outs — literal text matching directive, pipe-table or strikethrough syntax,
-  syntax is claimed (escapable — `spec/flavour.md`) — and one gap: a CommonMark image fits only as
+  and a code fence whose info string opens `adf:`, are claimed (each can be kept literal —
-  its own title-less paragraph; mid-text and titled images are error results, save an image inside
+  `spec/flavour.md`) — and one gap: a CommonMark image fits only as its own title-less paragraph;
-  another's description, which flattens into the alt text. Converting back yields the library's
+  mid-text and titled images are error results, save an image inside another's description, which
-  canonical spelling, which round-trips byte-identically — where it converts back at all: a parse
+  flattens into the alt text. Converting back yields the library's canonical spelling, which
-  succeeding is no promise of that, so keep the source until the way back succeeds.
+  round-trips byte-identically.
-  ``` ` `` ` ``` reads cleanly and then refuses.
 - Four CommonMark spellings parse without an error and build a document the reference
   implementation renders differently: `[](/url)` and `[]()` stay literal text against CommonMark's
   empty link, a list continuing past a marker change stays one list against CommonMark's two, a
@@ -225,28 +225,28 @@ emit refuses:
   text, which the spec requires and the reference itself breaks, nesting one `<a>` in the other.
   The first three are pinned `pending` in `corpus/commonmark-spec/exceptions.json`; the suite
   holds no example of the fourth.
-- Not every document converts back: `adfToMarkdown` is partial on valid ADF — a text node holding
+- Not every document converts back: `adfToMarkdown` refuses a document nesting past 500 levels, and
-  a carriage return, or a paragraph line beginning with a code span whose backticks read back as a
+  the node shapes the `unsupported-node-shape` row lists. Show the refusal and keep the document
-  fence. Show the refusal and keep the document read-only; saving markdown you could not produce
+  read-only; saving markdown you could not produce is the loss the round-trip exists to stop.
-  is the loss the round-trip exists to stop.
 - The pipe table narrows GFM's twice: every row opens with a pipe, so GFM's bare form is an error
   result rather than the prose it reads as, and an alignment colon in the delimiter row is an
   error too — ADF holds no column alignment. The trailing pipe is canonical output, optional in
   input.
 - Past that and `~~`, no GFM: an autolink literal and a `- [ ]` marker stay text, and a checklist
   is the `taskList` directive — `plainMarkdownToAdf` turns the marker into a `taskList`.
-- A document nested deeper than 500 levels is an error result, not a stack overflow.
+- A document nested deeper than 500 levels is an error result, not a stack overflow, and no call
+  loops forever on a string, or on a value `JSON.parse` or `structuredClone` builds.
 - The emitted formats are semver surface
   ([`docs/decisions.md`](https://gitea.larvit.se/larvit/adf-codec/src/branch/main/docs/decisions.md#the-formats-are-api)).
-- **`0.2.0`** — `htmlToAdf(adfToHtml(doc))` equals `doc`; fidelity HTML cannot express rides
+- **`0.2.0`** — `htmlToAdf(adfToHtml(doc))` deep-equals `doc`; fidelity HTML cannot express rides
   `data-*` attributes. Foreign HTML maps a documented element set, which markdown's raw HTML reads
   through as well, and a construct outside it is an error; well-formed HTML only — no tag-soup
   recovery.
 
 ## The package
 
-ESM only, no runtime dependencies, public npm. Built JavaScript with `.d.ts` beside it.
+Serves Goal 8. ESM only, no runtime dependencies, public npm. Built JavaScript with `.d.ts`
-Pure ECMAScript at an ES2022 baseline, reaching for no host API; the test suite runs under Node,
+beside it. Pure ECMAScript at an ES2022 baseline, reaching for no host API; the test suite runs
-Deno and Bun, and a headless Firefox converts the corpus through the built entrypoint.
+under Node, Deno and Bun, and a headless Firefox converts the corpus through the built entrypoint.
 Contract: [`docs/decisions.md`](https://gitea.larvit.se/larvit/adf-codec/src/branch/main/docs/decisions.md#any-es2022-engine), §Any
 ES2022 engine to §Public on npm.

browser-tests/convert-corpus.js

@@ -1,16 +1,18 @@
 try {
   const { adfToMarkdown, isAdfDocument, markdownToAdf } = await import('/dist/index.js')
+  // WebDriver's JSON reads -0 back as 0, so a document crosses as JSON text with -0 tagged; run.js revives it.
+  const spelled = (result) => (result.ok ? { ok: true, value: JSON.stringify(result.value, (_, value) => (Object.is(value, -0) ? '\u0000-0' : value)) } : result)
   window.convertCorpus = (corpus) => ({
     errors: corpus.errors.map(({ markdown, name }) => ({ name, parsed: markdownToAdf(markdown) })),
-    normalization: corpus.normalization.map(({ markdown, name }) => ({ name, parsed: markdownToAdf(markdown) })),
+    normalization: corpus.normalization.map(({ markdown, name }) => ({ name, parsed: spelled(markdownToAdf(markdown)) })),
     realPayloads: corpus.realPayloads.map(({ json, name }) => {
       const adf = JSON.parse(json)
       const emitted = adfToMarkdown(adf)
-      return { emitted, isDocument: isAdfDocument(adf), name, parsed: emitted.ok ? markdownToAdf(emitted.value) : undefined }
+      return { emitted, isDocument: isAdfDocument(adf), name, parsed: emitted.ok ? spelled(markdownToAdf(emitted.value)) : undefined }
     }),
     roundTrip: corpus.roundTrip.map(({ json, markdown, name }) => {
       const adf = JSON.parse(json)
-      return { emitted: adfToMarkdown(adf), isDocument: isAdfDocument(adf), name, parsed: markdownToAdf(markdown) }
+      return { emitted: adfToMarkdown(adf), isDocument: isAdfDocument(adf), name, parsed: spelled(markdownToAdf(markdown)) }
     }),
   })
 } catch (cause) {

browser-tests/run.js

@@ -2,7 +2,6 @@ import assert from 'node:assert/strict'
 import { createServer } from 'node:http'
 import { extname, join } from 'node:path'
 import { readFileSync, readdirSync } from 'node:fs'
-import { toEditorNormal } from '../dist/adf/editor-normal.js'
 
 const contentTypes = { '.html': 'text/html; charset=utf-8', '.js': 'text/javascript' }
 const driver = 'http://127.0.0.1:4444'
@@ -50,6 +49,11 @@ function fixtureNames(kind, extension) {
     .sort()
 }
 
+// convert-corpus.js tags -0 so it survives WebDriver's JSON.
+function revived(text) {
+  return JSON.parse(text, (_, value) => (value === '\u0000-0' ? -0 : value))
+}
+
 function refusal(result) {
   return result.ok ? '' : `${result.error.code}: ${result.error.message}`
 }
@@ -107,7 +111,7 @@ for (const [index, { json, markdown, name }] of corpus.roundTrip.entries()) {
     assert.ok(result.emitted.ok, `it did not emit — ${refusal(result.emitted)}`)
     assert.equal(result.emitted.value, markdown)
     assert.ok(result.parsed.ok, `it did not parse — ${refusal(result.parsed)}`)
-    assert.deepEqual(toEditorNormal(result.parsed.value), JSON.parse(json))
+    assert.deepEqual(revived(result.parsed.value), JSON.parse(json))
   })
 }
 
@@ -115,7 +119,7 @@ for (const [index, { name }] of corpus.normalization.entries()) {
   const result = results.normalization[index]
   checking(name, result, () => {
     assert.ok(result.parsed.ok, `it did not parse — ${refusal(result.parsed)}`)
-    assert.deepEqual(toEditorNormal(result.parsed.value), JSON.parse(fixture(name, '.json')))
+    assert.deepEqual(revived(result.parsed.value), JSON.parse(fixture(name, '.json')))
   })
 }
 
@@ -125,7 +129,7 @@ for (const [index, { json, name }] of corpus.realPayloads.entries()) {
     assert.ok(result.isDocument, `${name}.json is no ADF document`)
     assert.ok(result.emitted.ok, `it did not emit — ${refusal(result.emitted)}`)
     assert.ok(result.parsed.ok, `it did not parse back — ${refusal(result.parsed)}`)
-    assert.deepEqual(toEditorNormal(result.parsed.value), JSON.parse(json))
+    assert.deepEqual(revived(result.parsed.value), JSON.parse(json))
   })
 }
 

corpus/README.md

@@ -1,6 +1,6 @@
 # The corpus
 
-One directory per contract kind, each landing with its milestone:
+One directory per contract kind:
 
 - `round-trip/` — `<name>.json` + `<name>.md`: the markdown `adfToMarkdown` must emit for that
   document, byte for byte, and that `markdownToAdf` must read back to it (`docs/decisions.md` §The
@@ -16,11 +16,11 @@ One directory per contract kind, each landing with its milestone:
   is the suite; `refusals.json` pins each refusing example to its error `code`; `exceptions.json`
   pins each known divergence by `check`, `example`, `kind` and the exact `divergence`, with a
   `reason`. `kind` is `mark-model` (the permanent count divergence from ADF's mark-per-text-node
-  model), `unspellable` (parses but the flavour has no spelling) or `pending` (a parser gap a later
+  model) or `pending` (a parser gap).
-  milestone may close).
 
-JSON is editor-normal (`docs/decisions.md` §Equality is editor-normal), two-space indent, keys
+JSON is two-space indent, keys sorted, and a document read back must deep-equal the fixture's
-sorted. `spec.json` is the vendored, upstream machine-readable suite, byte-exact from
+(`docs/decisions.md` §Equality is deep). `spec.json` is the vendored, upstream machine-readable
-[spec.commonmark.org](https://spec.commonmark.org/0.31.2/spec.json) (CommonMark 0.31.2, © John
+suite, byte-exact from [spec.commonmark.org](https://spec.commonmark.org/0.31.2/spec.json)
-MacFarlane, [CC-BY-SA-4.0](https://creativecommons.org/licenses/by-sa/4.0/)), and is not
+(CommonMark 0.31.2, © John MacFarlane,
-re-serialized by the corpus gate.
+[CC-BY-SA-4.0](https://creativecommons.org/licenses/by-sa/4.0/)), and is not re-serialized by the
+corpus gate.

corpus/commonmark-spec/exceptions.json

@@ -13,27 +13,6 @@
     "kind": "pending",
     "reason": "A list continuing past a marker change renders as two lists, the parser opens one."
   },
-  {
-    "check": "fixpoint",
-    "divergence": "unspellable-line-start",
-    "example": 330,
-    "kind": "unspellable",
-    "reason": "A paragraph opens with a code span whose backticks read back as a fence."
-  },
-  {
-    "check": "fixpoint",
-    "divergence": "unspellable-line-start",
-    "example": 331,
-    "kind": "unspellable",
-    "reason": "A paragraph opens with a code span whose backticks read back as a fence."
-  },
-  {
-    "check": "fixpoint",
-    "divergence": "unspellable-line-start",
-    "example": 340,
-    "kind": "unspellable",
-    "reason": "A paragraph opens with a code span whose backticks read back as a fence."
-  },
   {
     "check": "count",
     "divergence": "em 2/1",

corpus/errors/carry-fence-type-spellable.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/carry-fence-type-spellable.md

@@ -0,0 +1,5 @@
+```adf:
+{
+  "type": "blockCard"
+}
+```

corpus/errors/carry-fence-type-unspellable.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/carry-fence-type-unspellable.md

@@ -0,0 +1,3 @@
+```adf:\\
+{}
+```

corpus/errors/carry-fence-type.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/carry-fence-type.md

@@ -0,0 +1,5 @@
+```adf:blockCard
+{
+  "type": "blockCard"
+}
+```

corpus/errors/carry-invalid-json.md

@@ -1,3 +1,3 @@
-```carry
+```adf:blockCard
-{"type":
+{"attrs":
 ```

corpus/errors/code-block-empty-attrs-fence-language.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/code-block-empty-attrs-fence-language.md

@@ -0,0 +1,8 @@
+!adf:codeBlock {attrs=empty}
+```js
+a
+```
+```js
+b
+```
+!adf:/codeBlock

corpus/errors/code-block-empty-fence.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/code-block-empty-fence.md

@@ -0,0 +1,7 @@
+!adf:codeBlock
+```
+a
+```
+```
+```
+!adf:/codeBlock

corpus/errors/code-block-fence-languages.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/code-block-fence-languages.md

@@ -0,0 +1,8 @@
+!adf:codeBlock
+```js
+a
+```
+```ts
+b
+```
+!adf:/codeBlock

corpus/errors/directive-slot-carried-marks.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/directive-slot-carried-marks.md

@@ -0,0 +1 @@
+!adf:status[!adf:carry{json="{\"marks\":[],\"text\":\"x\",\"type\":\"text\"}"}]

corpus/errors/document-directive-bare.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/document-directive-bare.md

@@ -0,0 +1 @@
+!adf:doc

corpus/errors/document-directive-misplaced.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/document-directive-misplaced.md

@@ -0,0 +1,3 @@
+!adf:doc {content=none}
+
+Text.

corpus/errors/empty-attrs-with-attributes.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/empty-attrs-with-attributes.md

@@ -0,0 +1,3 @@
+!adf:panel info {attrs=empty}
+Text.
+!adf:/panel

corpus/errors/empty-content-with-body.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/empty-content-with-body.md

@@ -0,0 +1,3 @@
+!adf:paragraph {content=empty}
+Text.
+!adf:/paragraph

corpus/errors/empty-key-value.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/empty-key-value.md

@@ -0,0 +1,3 @@
+!adf:paragraph {attrs=none}
+Text.
+!adf:/paragraph

corpus/errors/empty-marks-wrapped.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/empty-marks-wrapped.md

@@ -0,0 +1 @@
+**!adf:date{marks=empty}**

corpus/errors/text-break-attributes.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/text-break-attributes.md

@@ -0,0 +1 @@
+a!adf:textBreak{x=y}b

corpus/errors/text-break-content.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/text-break-content.md

@@ -0,0 +1 @@
+a!adf:textBreak[x]b

corpus/errors/text-break-marks-differ.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/text-break-marks-differ.md

@@ -0,0 +1 @@
+**a**!adf:textBreak{}b

corpus/errors/text-break-misplaced.error

@@ -0,0 +1 @@
+unsupported-node-shape

corpus/errors/text-break-misplaced.md

@@ -0,0 +1 @@
+!adf:textBreak{}Hello

corpus/round-trip/block-nodes/code-block-carriage-return.json

@@ -0,0 +1,15 @@
+{
+  "content": [
+    {
+      "content": [
+        {
+          "text": "a\r\nb",
+          "type": "text"
+        }
+      ],
+      "type": "codeBlock"
+    }
+  ],
+  "type": "doc",
+  "version": 1
+}

corpus/round-trip/block-nodes/code-block-carriage-return.md

@@ -0,0 +1,10 @@
+```adf:codeBlock
+{
+  "content": [
+    {
+      "text": "a\r\nb",
+      "type": "text"
+    }
+  ]
+}
+```

corpus/round-trip/block-nodes/code-block-carry.json

@@ -14,7 +14,19 @@
     },
     {
       "attrs": {
-        "language": "carry"
+        "language": "adf:blockCard"
+      },
+      "content": [
+        {
+          "text": "{\n  \"attrs\": {}\n}",
+          "type": "text"
+        }
+      ],
+      "type": "codeBlock"
+    },
+    {
+      "attrs": {
+        "language": "adf:"
       },
       "content": [
         {

corpus/round-trip/block-nodes/code-block-carry.md

@@ -1,12 +1,18 @@
-!adf:codeBlock {language=carry}
+```carry
-```
 {
   "type": "blockCard"
 }
 ```
+
+!adf:codeBlock {language="adf:blockCard"}
+```
+{
+  "attrs": {}
+}
+```
 !adf:/codeBlock
 
-!adf:codeBlock {language=carry}
+!adf:codeBlock {language="adf:"}
 ````
 ```
 ````

corpus/round-trip/block-nodes/code-block-text-nodes.json

@@ -0,0 +1,56 @@
+{
+  "content": [
+    {
+      "attrs": {
+        "language": "js"
+      },
+      "content": [
+        {
+          "text": "const a = 1\n",
+          "type": "text"
+        },
+        {
+          "text": "const b = 2",
+          "type": "text"
+        }
+      ],
+      "type": "codeBlock"
+    },
+    {
+      "content": [
+        {
+          "text": "a",
+          "type": "text"
+        },
+        {
+          "text": "```",
+          "type": "text"
+        },
+        {
+          "text": "\n",
+          "type": "text"
+        }
+      ],
+      "type": "codeBlock"
+    },
+    {
+      "attrs": {
+        "language": "has`tick",
+        "wrap": true
+      },
+      "content": [
+        {
+          "text": "x",
+          "type": "text"
+        },
+        {
+          "text": " y ",
+          "type": "text"
+        }
+      ],
+      "type": "codeBlock"
+    }
+  ],
+  "type": "doc",
+  "version": 1
+}

corpus/round-trip/block-nodes/code-block-text-nodes.md

@@ -0,0 +1,31 @@
+!adf:codeBlock
+```js
+const a = 1
+
+```
+```js
+const b = 2
+```
+!adf:/codeBlock
+
+!adf:codeBlock
+```
+a
+```
+````
+```
+````
+```
+
+
+```
+!adf:/codeBlock
+
+!adf:codeBlock {language="has\u0060tick" wrap=true}
+```
+x
+```
+```
+ y 
+```
+!adf:/codeBlock

corpus/round-trip/block-nodes/document-without-content.json

@@ -0,0 +1,4 @@
+{
+  "type": "doc",
+  "version": 1
+}

corpus/round-trip/block-nodes/document-without-content.md

@@ -0,0 +1 @@
+!adf:doc {content=none}

corpus/round-trip/block-nodes/empty-keys.json

@@ -0,0 +1,96 @@
+{
+  "content": [
+    {
+      "content": [],
+      "type": "paragraph"
+    },
+    {
+      "attrs": {},
+      "content": [
+        {
+          "text": "Plain words.",
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    },
+    {
+      "content": [],
+      "type": "rule"
+    },
+    {
+      "attrs": {
+        "level": 2
+      },
+      "content": [
+        {
+          "text": "Title",
+          "type": "text"
+        }
+      ],
+      "marks": [],
+      "type": "heading"
+    },
+    {
+      "attrs": {
+        "panelType": "info"
+      },
+      "content": [],
+      "type": "panel"
+    },
+    {
+      "content": [
+        {
+          "attrs": {},
+          "content": [
+            {
+              "content": [
+                {
+                  "text": "Item",
+                  "type": "text"
+                }
+              ],
+              "type": "paragraph"
+            }
+          ],
+          "type": "listItem"
+        },
+        {
+          "content": [
+            {
+              "content": [
+                {
+                  "text": "Next",
+                  "type": "text"
+                }
+              ],
+              "type": "paragraph"
+            }
+          ],
+          "type": "listItem"
+        }
+      ],
+      "type": "bulletList"
+    },
+    {
+      "content": [],
+      "type": "codeBlock"
+    },
+    {
+      "attrs": {
+        "language": "js"
+      },
+      "marks": [],
+      "type": "codeBlock"
+    },
+    {
+      "attrs": {
+        "language": "js"
+      },
+      "content": [],
+      "type": "codeBlock"
+    }
+  ],
+  "type": "doc",
+  "version": 1
+}

corpus/round-trip/block-nodes/empty-keys.md

@@ -0,0 +1,35 @@
+!adf:paragraph {content=empty}
+!adf:/paragraph
+
+!adf:paragraph {attrs=empty}
+Plain words.
+!adf:/paragraph
+
+!adf:rule {content=empty}
+
+!adf:heading {level=2 marks=empty}
+Title
+!adf:/heading
+
+!adf:panel info {content=empty}
+!adf:/panel
+
+!adf:bulletList
+!adf:listItem {attrs=empty}
+Item
+!adf:/listItem
+!adf:listItem
+Next
+!adf:/listItem
+!adf:/bulletList
+
+!adf:codeBlock {content=empty}
+!adf:/codeBlock
+
+!adf:codeBlock {marks=empty}
+```js
+```
+!adf:/codeBlock
+
+!adf:codeBlock {content=empty language=js}
+!adf:/codeBlock

corpus/round-trip/combinations/carry-attributes.md

@@ -1,4 +1,4 @@
-```carry
+```adf:panel
 {
   "attrs": {
     "rounded": true
@@ -13,12 +13,11 @@
       ],
       "type": "paragraph"
     }
-  ],
+  ]
-  "type": "panel"
 }
 ```
 
-```carry
+```adf:panel
 {
   "attrs": {
     "panelType": "extra info"
@@ -33,8 +32,7 @@
       ],
       "type": "paragraph"
     }
-  ],
+  ]
-  "type": "panel"
 }
 ```
 

corpus/round-trip/combinations/negative-zero.json

@@ -0,0 +1,83 @@
+{
+  "content": [
+    {
+      "attrs": {
+        "order": -0
+      },
+      "content": [
+        {
+          "content": [
+            {
+              "content": [
+                {
+                  "text": "First",
+                  "type": "text"
+                }
+              ],
+              "type": "paragraph"
+            }
+          ],
+          "type": "listItem"
+        }
+      ],
+      "type": "orderedList"
+    },
+    {
+      "attrs": {
+        "level": -0
+      },
+      "content": [
+        {
+          "text": "Title",
+          "type": "text"
+        }
+      ],
+      "type": "heading"
+    },
+    {
+      "attrs": {
+        "extensionKey": "toc",
+        "extensionType": "com.atlassian.confluence.macro.core",
+        "parameters": {
+          "maxLevel": -0
+        }
+      },
+      "type": "extension"
+    },
+    {
+      "content": [
+        {
+          "attrs": {
+            "data": [
+              -0
+            ],
+            "url": "https://example.com/"
+          },
+          "type": "inlineCard"
+        },
+        {
+          "marks": [
+            {
+              "attrs": {
+                "color": "#000000",
+                "size": -0
+              },
+              "type": "border"
+            }
+          ],
+          "text": "x",
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    },
+    {
+      "attrs": {
+        "x": -0
+      },
+      "type": "blockCard"
+    }
+  ],
+  "type": "doc",
+  "version": 1
+}

corpus/round-trip/combinations/negative-zero.md

@@ -0,0 +1,21 @@
+!adf:orderedList {order=-0}
+!adf:listItem
+First
+!adf:/listItem
+!adf:/orderedList
+
+!adf:heading {level=-0}
+Title
+!adf:/heading
+
+!adf:extension {extensionKey=toc extensionType="com.atlassian.confluence.macro.core" parameters="{\"maxLevel\":-0}"}
+
+!adf:inlineCard{data="[-0]" url="https://example.com/"}!adf:border[x]{color="#000000" size=-0}
+
+```adf:blockCard
+{
+  "attrs": {
+    "x": -0
+  }
+}
+```

corpus/round-trip/commonmark-subset/code-span-line-start.json

@@ -0,0 +1,20 @@
+{
+  "content": [
+    {
+      "content": [
+        {
+          "marks": [
+            {
+              "type": "code"
+            }
+          ],
+          "text": "``",
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    }
+  ],
+  "type": "doc",
+  "version": 1
+}

corpus/round-trip/commonmark-subset/code-span-line-start.md

@@ -0,0 +1 @@
+``` `` ```

corpus/round-trip/commonmark-subset/document-empty.json

@@ -1,4 +1,5 @@
 {
+  "content": [],
   "type": "doc",
   "version": 1
 }

corpus/round-trip/inline-nodes/empty-keys.json

@@ -0,0 +1,98 @@
+{
+  "content": [
+    {
+      "content": [
+        {
+          "attrs": {},
+          "type": "date"
+        },
+        {
+          "text": " ",
+          "type": "text"
+        },
+        {
+          "content": [],
+          "type": "date"
+        }
+      ],
+      "type": "paragraph"
+    },
+    {
+      "content": [
+        {
+          "text": "a",
+          "type": "text"
+        },
+        {
+          "marks": [],
+          "type": "hardBreak"
+        },
+        {
+          "text": "b",
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    },
+    {
+      "content": [
+        {
+          "attrs": {
+            "id": "x",
+            "text": "@M"
+          },
+          "content": [],
+          "type": "mention"
+        }
+      ],
+      "type": "paragraph"
+    },
+    {
+      "content": [
+        {
+          "text": "bare",
+          "type": "text"
+        },
+        {
+          "marks": [],
+          "text": "marked",
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    },
+    {
+      "content": [
+        {
+          "marks": [
+            {
+              "attrs": {},
+              "type": "em"
+            }
+          ],
+          "text": "x",
+          "type": "text"
+        },
+        {
+          "text": " and ",
+          "type": "text"
+        },
+        {
+          "attrs": {
+            "shortName": ":a:"
+          },
+          "marks": [
+            {
+              "attrs": {},
+              "type": "strong"
+            }
+          ],
+          "type": "emoji"
+        }
+      ],
+      "type": "paragraph"
+    }
+  ],
+  "type": "doc",
+  "version": 1
+}

corpus/round-trip/inline-nodes/empty-keys.md

@@ -0,0 +1,9 @@
+!adf:date{attrs=empty} !adf:date{content=empty}
+
+a!adf:hardBreak{marks=empty}b
+
+!adf:mention[@M]{content=empty id=x}
+
+bare!adf:carry{json="{\"marks\":[],\"text\":\"marked\",\"type\":\"text\"}"}
+
+!adf:carry{json="{\"marks\":[{\"attrs\":{},\"type\":\"em\"}],\"text\":\"x\",\"type\":\"text\"}"} and !adf:carry{json="{\"attrs\":{\"shortName\":\":a:\"},\"marks\":[{\"attrs\":{},\"type\":\"strong\"}],\"type\":\"emoji\"}"}

corpus/round-trip/inline-nodes/text-break.json

@@ -0,0 +1,154 @@
+{
+  "content": [
+    {
+      "content": [
+        {
+          "text": "Hello, ",
+          "type": "text"
+        },
+        {
+          "text": "world",
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    },
+    {
+      "content": [
+        {
+          "marks": [
+            {
+              "type": "strong"
+            }
+          ],
+          "text": "Hello, ",
+          "type": "text"
+        },
+        {
+          "marks": [
+            {
+              "type": "strong"
+            }
+          ],
+          "text": "world",
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    },
+    {
+      "content": [
+        {
+          "marks": [
+            {
+              "type": "code"
+            }
+          ],
+          "text": "a",
+          "type": "text"
+        },
+        {
+          "marks": [
+            {
+              "type": "code"
+            }
+          ],
+          "text": "b",
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    },
+    {
+      "content": [
+        {
+          "marks": [
+            {
+              "attrs": {
+                "href": "https://example.com/"
+              },
+              "type": "link"
+            }
+          ],
+          "text": "a",
+          "type": "text"
+        },
+        {
+          "marks": [
+            {
+              "attrs": {
+                "href": "https://example.com/"
+              },
+              "type": "link"
+            }
+          ],
+          "text": "b",
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    },
+    {
+      "content": [
+        {
+          "text": "Line\n",
+          "type": "text"
+        },
+        {
+          "text": "next",
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    },
+    {
+      "content": [
+        {
+          "marks": [
+            {
+              "type": "underline"
+            }
+          ],
+          "text": "a",
+          "type": "text"
+        },
+        {
+          "marks": [
+            {
+              "type": "underline"
+            }
+          ],
+          "text": "b",
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    },
+    {
+      "content": [
+        {
+          "marks": [
+            {
+              "attrs": {},
+              "type": "underline"
+            }
+          ],
+          "text": "a",
+          "type": "text"
+        },
+        {
+          "marks": [
+            {
+              "type": "underline"
+            }
+          ],
+          "text": "b",
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    }
+  ],
+  "type": "doc",
+  "version": 1
+}

corpus/round-trip/inline-nodes/text-break.md

@@ -0,0 +1,13 @@
+Hello, !adf:textBreak{}world
+
+**Hello, !adf:textBreak{}world**
+
+`a`!adf:textBreak{}`b`
+
+[a!adf:textBreak{}b](https://example.com/)
+
+Line!adf:text{text="\n"}!adf:textBreak{}next
+
+!adf:underline[a!adf:textBreak{}b]
+
+!adf:underline[a]{attrs=empty}!adf:underline[b]

corpus/round-trip/inline-nodes/text-carriage-return-null.json

@@ -0,0 +1,43 @@
+{
+  "content": [
+    {
+      "content": [
+        {
+          "text": "a\r\nb\u0000c",
+          "type": "text"
+        },
+        {
+          "marks": [
+            {
+              "attrs": {
+                "href": "https://example.com/",
+                "title": "t\u0000"
+              },
+              "type": "link"
+            }
+          ],
+          "text": "link",
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    },
+    {
+      "content": [
+        {
+          "attrs": {
+            "color": "neutral",
+            "text": "a\nb"
+          },
+          "type": "status"
+        },
+        {
+          "type": "text"
+        }
+      ],
+      "type": "paragraph"
+    }
+  ],
+  "type": "doc",
+  "version": 1
+}

corpus/round-trip/inline-nodes/text-carriage-return-null.md

@@ -0,0 +1,3 @@
+a
!adf:text{text="\n"}b!adf:text{text="\u0000"}c!adf:link[link]{href="https://example.com/" title="t\u0000"}
+
+!adf:carry{json="{\"attrs\":{\"color\":\"neutral\",\"text\":\"a\\nb\"},\"type\":\"status\"}"}!adf:carry{json="{\"type\":\"text\"}"}

corpus/round-trip/opaque-carry/carry-in-wrappers.md

@@ -1,17 +1,15 @@
-> ```carry
+> ```adf:blockCard
 > {
 >   "attrs": {
 >     "url": "https://example.com/quoted"
->   },
+>   }
->   "type": "blockCard"
 > }
 > ```
 
-- ```carry
+- ```adf:blockCard
   {
     "attrs": {
       "url": "https://example.com/listed"
-    },
+    }
-    "type": "blockCard"
   }
   ```

corpus/round-trip/opaque-carry/code-block-children.json

@@ -0,0 +1,35 @@
+{
+  "content": [
+    {
+      "attrs": {
+        "language": "js"
+      },
+      "content": [
+        {
+          "marks": [
+            {
+              "type": "strong"
+            }
+          ],
+          "text": "const a = 1",
+          "type": "text"
+        }
+      ],
+      "type": "codeBlock"
+    },
+    {
+      "content": [
+        {
+          "text": "a",
+          "type": "text"
+        },
+        {
+          "type": "hardBreak"
+        }
+      ],
+      "type": "codeBlock"
+    }
+  ],
+  "type": "doc",
+  "version": 1
+}

corpus/round-trip/opaque-carry/code-block-children.md

@@ -0,0 +1,32 @@
+```adf:codeBlock
+{
+  "attrs": {
+    "language": "js"
+  },
+  "content": [
+    {
+      "marks": [
+        {
+          "type": "strong"
+        }
+      ],
+      "text": "const a = 1",
+      "type": "text"
+    }
+  ]
+}
+```
+
+```adf:codeBlock
+{
+  "content": [
+    {
+      "text": "a",
+      "type": "text"
+    },
+    {
+      "type": "hardBreak"
+    }
+  ]
+}
+```

corpus/round-trip/opaque-carry/unknown-block.md

@@ -1,23 +1,21 @@
-```carry
+```adf:blockCard
 {
   "attrs": {
     "url": "https://example.com/roadmap"
-  },
+  }
-  "type": "blockCard"
 }
 ```
 
 !adf:panel info
 The card below has no spelling yet.
 
-```carry
+```adf:embedCard
 {
   "attrs": {
     "layout": "wide",
     "url": "https://example.com/board",
     "width": 100
-  },
+  }
-  "type": "embedCard"
 }
 ```
 !adf:/panel

corpus/round-trip/opaque-carry/unknown-type-spelling.json

@@ -0,0 +1,21 @@
+{
+  "content": [
+    {
+      "attrs": {
+        "url": "https://example.com/"
+      },
+      "type": "has`tick"
+    },
+    {
+      "type": ""
+    },
+    {
+      "type": " padded"
+    },
+    {
+      "type": "two words"
+    }
+  ],
+  "type": "doc",
+  "version": 1
+}

corpus/round-trip/opaque-carry/unknown-type-spelling.md

@@ -0,0 +1,24 @@
+```adf:
+{
+  "attrs": {
+    "url": "https://example.com/"
+  },
+  "type": "has`tick"
+}
+```
+
+```adf:
+{
+  "type": ""
+}
+```
+
+```adf:
+{
+  "type": " padded"
+}
+```
+
+```adf:two words
+{}
+```

docs/decisions.md

@@ -14,7 +14,7 @@ a backslash reach them intact; what the flavour cannot spell reduces ADF→ADF a
 2026-08-23, real payloads 2026-09-15, the maintainer. Goal 1. Valid while a consumer saves back
 through the lossless pair.
 
-`markdownToAdf(adfToMarkdown(doc))` and `htmlToAdf(adfToHtml(doc))` must equal `doc` — anything
+`markdownToAdf(adfToMarkdown(doc))` and `htmlToAdf(adfToHtml(doc))` must deep-equal `doc` — anything
 less silently destroys content an editor could not represent, in a document it did not author.
 When losslessness and readability conflict, losslessness wins. Round-trip equality is a property
 tested over a checked-in corpus (`corpus/README.md`), not a claim made in prose. Its real payloads
@@ -23,40 +23,103 @@ sanitized and a mention keeps the test user's real account id.
 
 ## Markdown in is a canonical fixpoint
 
-2026-08-23, the maintainer. Goals 1 and 3. Valid while markdown input may be written by hand.
+2026-08-23, the maintainer; every parsed document has converted back since 2026-10-04. Goals 1 and
+5. Valid while markdown input may be written by hand.
 
 The other direction is a canonical fixpoint, not byte-identity: human markdown normalizes, the way
-back yields the library's canonical spelling, and that spelling round-trips byte-identically —
+back yields the library's canonical spelling, and that spelling round-trips byte-identically.
-where there is a way back. CommonMark spells some things the flavour has no escape for — a
-paragraph opening with a code span whose backticks read back as a fence — so a parse succeeding
-does not imply a spellable document; `corpus/commonmark-spec/exceptions.json` names those.
 
-## Equality is editor-normal
+## Equality is deep
 
-2026-08-24, the maintainer. Goal 1. Valid while markdown cannot tell apart the ADF shapes this
+2026-08-24, deep 2026-10-03, the maintainer. Goal 1. Valid while a pipeline or a bot can build a
-merges.
+shape the editor would not.
 
-"Equals" is structural equality over editor-normal ADF — adjacent text nodes with identical marks
+"Equals" is deep equality over the document's JSON values: `assert.deepStrictEqual` on plain objects
-and no attributes merged, JSON number semantics, an empty attrs object, marks array or content
+as `JSON.parse` builds them, since ADF is JSON. Every key and value in `doc` counts, including two
-array the absent key — the only domain markdown can restore.
+adjacent text nodes, an empty `attrs`, `content` or `marks`, and `-0`. Neither side is normalized.
-Replaced by deep equality with `todo.md` 40 (2026-09-28, the maintainer).
+CommonMark's spelling stays wherever a document holds none of those shapes. The plain reader builds
+what is written, as `markdownToAdf` does. Only the plain writer is lossy: its reduction reads and
+writes editor-normal ADF — adjacent text nodes of identical marks and no attributes merged, `-0` as
+`0`, and an empty `attrs`, `content` or `marks` the absent key, except the doc's `content`, which
+ADF's schema requires — so two documents the editor holds equal write the same plain markdown.
+
+## `!adf:textBreak{}` parts text CommonMark would join
+
+2026-10-03, the maintainer. Goal 1. Valid while CommonMark reads adjacent text as one run.
+
+Two adjacent text nodes CommonMark would read back as one are parted by the reserved inline leaf
+`!adf:textBreak{}`, mirroring `!adf:listBreak`: a leaf building no node keeps both nodes and asks
+nothing of the text around it. A code span holds no directive, so the spans close and reopen
+around the leaf. The grammar: `spec/flavour.md` §Inline nodes, **Adjacent text nodes**.
+
+## An empty key spells `empty`
+
+2026-10-03, a writer panel and the maintainer. Goals 1 and 6. Valid while no attribute value
+spells an empty object or array.
+
+An `attrs`, `content` or `marks` key holding an empty object or array is the reserved key with the
+bare value `empty`, so a container opener and closer with nothing between them stays the node
+holding no `content` key. A writer panel chose the spelling, 5 of 7. The grammar: `spec/flavour.md`
+§Directives, **Attributes**, and §Marks.
+
+## `-0` is spelled `-0`
+
+2026-10-03, the maintainer. Goal 1. Valid while JSON's own serialization writes `-0` as `0`.
+
+`-0` is spelled `-0` wherever the flavour writes a number or a JSON value, since JSON's grammar
+reads it back as `-0`. The grammar: `spec/flavour.md` §Block nodes and §The CommonMark blocks.
+
+## Empty markdown is a document of no blocks
+
+2026-10-03, a writer panel and the maintainer. Goals 1 and 6. Valid while ADF's schema requires
+`content` on `doc`.
+
+Markdown holding no block reads as `{ content: [], type: 'doc', version: 1 }`, the document
+`spec/adf-schema/full.json` requires. A document holding no `content` key is
+`!adf:doc {content=none}` as its only block, and a named error anywhere else. The writer panel split
+4 for `none` and 3 for `absent`, and the maintainer chose `none`; all seven rejected a bare
+`!adf:doc`.
 
 ## Unknown nodes ride the carry
 
-2026-08-23, extended to misplaced known nodes 2026-08-26, the maintainer. Goal 1. Valid while ADF
+2026-08-23, extended to misplaced known nodes 2026-08-26 and to code block children 2026-10-03, the
-holds nodes, or node positions, this library does not spell.
+maintainer. Goal 1. Valid while ADF holds nodes, or node positions, this library does not spell.
 
 An unknown ADF node is carried opaquely — raw JSON rides a dedicated syntax in both formats and
 restores to a deep-equal node. The round-trip holds for documents newer than the library. So does
 a known node no section spells where it stands: a markdown serializer spells a node by type without
-checking its position, and refusing loses a document ADF itself keeps in an `unsupportedBlock`.
+checking its position, and refusing loses a document ADF itself keeps in an `unsupportedBlock`. A
-Where a container's own spelling cannot hold the child it has — a `bulletList` outside `listItem`,
+`codeBlock` holding a child no fence holds — anything but a text node carrying no marks, `attrs` or
-a `codeBlock` outside text — the error result names that instead.
+`content` — rides the carry whole.
+
+## The carry fence names the node type
+
+2026-10-03, the maintainer. Goals 1 and 6. Valid while a code fence's info string reads back
+verbatim.
+
+The block carry is a code fence whose info string `adf:<type>` names the node's type, its body the
+node's JSON without `type`: ```` ```adf:blockCard ````. A type no info string carries back — by the
+rule a code language follows — leaves the info string `adf:` and keeps `type` in the body. Every
+info string opening `adf:` is reserved, so a `codeBlock` whose language opens so takes the
+`language` attribute, and `carry` is an ordinary language. A body holding `type` under a named type,
+or a fence whose info string is `adf:` alone while its body's `type` could be spelled in the info
+string, is `unsupported-node-shape`. The reservation claims a fence CommonMark reads as code until
+`todo.md` item 43 gives CommonMark its own reader.
+
+## A code block is a fence per text node
+
+2026-10-03, the maintainer. Goal 1. Valid while ADF holds a code block's text in more than one
+node.
+
+A `codeBlock` holding several text nodes is the `!adf:codeBlock` container holding one fence per
+node, so each node keeps its own text. The fences carry one info string, since ADF holds one
+language, and none is empty beside another, since a text node holds text. The grammar:
+`spec/flavour.md` §The CommonMark blocks, the `codeBlock` bullet.
 
 ## Foreign HTML sorts three ways
 
-2026-08-23, the sort 2026-09-20, the maintainer. Goals 1, 3 and 6. Valid while ADF holds no node
+2026-08-23, the sort 2026-09-20, the maintainer. Goals 1 and 5. Valid while ADF holds no node
-for a bare container, a comment or a script. Lands with `todo.md` 6.
+for a bare container, a comment or a script. Lands with `todo.md` item 6.
 
 Every foreign element `htmlToAdf` and `markdownToAdf` read sorts one of three ways, never a silent
 drop of content:
@@ -76,14 +139,14 @@ than they buy.
 
 ## Names stay text
 
-2026-08-23, the maintainer. Goal 7. Valid while resolving a name to an id needs I/O.
+2026-08-23, the maintainer. Goal 8. Valid while resolving a name to an id needs I/O.
 
 A bare `@name` or `:smile:` in typed text stays a text node. Only directives produce
 mention/emoji/media nodes; resolving names to ids is the consumer's job.
 
 ## Directives under `!adf:`
 
-2026-08-23, prefixed `!adf:` 2026-09-16, the maintainer. Goals 3 and 4. Valid while prose does not
+2026-08-23, prefixed `!adf:` 2026-09-16, the maintainer. Goals 5 and 6. Valid while prose does not
 write `!adf:`.
 
 Directives are one grammar for everything markdown lacks, namespaced under `!adf:`:
@@ -94,21 +157,23 @@ opener nests by itself and leaf versus container falls out of the node's content
 
 ## CommonMark is a subset
 
-2026-08-23, the maintainer. Goal 3. Valid while prose rarely writes the shapes the carve-outs claim.
+2026-08-23, the maintainer. Goal 5. Valid while prose rarely writes the shapes the carve-outs claim.
 
 Plain CommonMark is a subset, with carve-outs (`spec/flavour.md`): literal text shaped like a
-directive, a pipe table or a `~~` pair is claimed — plus one image gap.
+directive, a pipe table or a `~~` pair is claimed, and so is a code fence whose info string opens
+`adf:` (§The carry fence names the node type) — plus one image gap. `todo.md` item 43 ends the
+claims, giving CommonMark its own reader, and `todo.md` item 65 ends the image gap.
 
 ## Tables
 
-2026-08-23, the maintainer. Goal 4. Valid while a pipe table holds only one header row and inline
+2026-08-23, the maintainer. Goal 6. Valid while a pipe table holds only one header row and inline
 cells.
 
 One header row plus plain inline cells → pipe table; anything richer → directive form.
 
 ## Links
 
-2026-09-13, nesting 2026-09-17, the maintainer. Goals 1 and 4. Valid while CommonMark's link
+2026-09-13, nesting 2026-09-17, the maintainer. Goals 1 and 6. Valid while CommonMark's link
 syntax is what readers edit.
 
 `[text](url "title")`, or `<url>` for a bare autolink-shaped text, wherever CommonMark spells the
@@ -127,24 +192,38 @@ accepted.
 
 ## Plain task ids come from position
 
-2026-09-26, the maintainer. Goals 5 and 7. Valid while a site rejects a task node with no
+2026-09-26, spelling 2026-09-29, the maintainer. Goals 7 and 8. Valid while a site rejects a task
-`localId`. Lands with `todo.md` 10f.
+node with no `localId`.
 
-`plainMarkdownToAdf` gives each `taskList`, `taskItem` and `blockTaskItem` a `localId` from its
+`plainMarkdownToAdf` gives each `taskList`, `taskItem` and `blockTaskItem` lacking one a `localId`
-position in document order, unique within the document and minted with no host API, so a site
+in the editor's UUID v4 shape, hashed from the whole markdown and the node's order among those it
-rejecting a missing `localId` takes the document and the same markdown reads to the same ids every
+mints, skipping any id the document holds: the same markdown reads to the same ids every run,
-run.
+different markdown to different ids. The same markdown pasted twice into one document repeats its
+ids: determinism wins over that case. A node the carry restores stays deep-equal (§Unknown nodes ride the carry): its
+ids are only skipped.
+
+## A callout title keeps its link targets
+
+2026-09-29, the maintainer. Goals 6 and 7. Valid while an expand's `title` is a string.
+
+`plainMarkdownToAdf` writes a link in a folded callout's title as its text and its target in
+parentheses: `> [!faq]- See [x](http://y)` reads to the title `See x (http://y)`. A link whose text
+is its target, with or without `mailto:`, keeps its text alone: `<http://y>` titles `http://y`,
+`<a@b.c>` `a@b.c` — three persona readers agreeing, 2026-09-30.
 
 ## The plain flavour's spellings
 
-2026-09-14, panels 2026-09-25, the maintainer. Goal 5. Valid while GitHub's renderer is the one the
+2026-09-14, panels 2026-09-25 and 2026-09-29, the maintainer. Goals 6 and 7. Valid while GitHub's
-audience's markdown is read in.
+renderer is the one the audience's markdown is read in.
 
 README §Plain markdown's rows come from a survey of GitHub, GitLab, Gitea, Obsidian, Pandoc,
 MkDocs, Docusaurus, Typora, Joplin, Logseq, Bear, Notion, Azure DevOps and Discord, GitHub's
-renderer confirming each shape. Reader panels settled `error` as an error panel and the `==`
+renderer confirming each shape. Reader panels settled `error` as an error panel, the `==` bounds
-bounds (3 of 3), the external image's two forms (6 of 7), the omission notes and a rule opening a
+(3 of 3) and a Han, Hangul, kana, Thai, Lao, Khmer or Myanmar character on either side bounding a
-list item dropping (3 of 3), and a list's numbering overflowing into bullets (3 of 3, 5 of 7).
+delimiter, so `は==日本語==で` (3 of 3), `==한국어==에서만` and `iPhone==専用==` (6 of 7) highlight,
+the external image's two forms (6 of 7), a rule opening a list item dropping and the omission
+notes (3 of 3), and a list's numbering overflowing into bullets (3 of 3, 5 of 7).
+An omission note reads as the converter's, never as the author's.
 Reading takes other tools' spellings, since it reads their output and writes none of them.
 Rejected: `~sub~` and `^sup^` (`~2~` is a strike on GitHub, so `subsup` drops), underline and colour
 spellings, raw HTML (`<details>`, `<mark>`), MkDocs `!!!` and the `:::` admonition family,
@@ -153,7 +232,7 @@ past `[x]`/`[ ]`, and lifting bare URLs, `@name`, `:shortcode:` or ISO dates int
 
 ## The HTML dialect
 
-2026-08-23, the maintainer. Goals 4 and 7. Valid while HTML output is read by consumers styling it
+2026-08-23, the maintainer. Goals 6 and 8. Valid while HTML output is read by consumers styling it
 themselves.
 
 The HTML dialect mirrors the markdown flavour: semantic elements, stable `adf-*` classes, `data-*`
@@ -161,7 +240,7 @@ for what HTML cannot express, text always escaped. No stylesheet ships.
 
 ## No runtime dependencies
 
-2026-08-23, the maintainer. Goal 7. Valid while ~20 lines of own code, or a vendored table, do each
+2026-08-23, the maintainer. Goal 8. Valid while ~20 lines of own code, or a vendored table, do each
 job a dependency would.
 
 `dependencies` is empty. A runtime dependency enters only through an entry here stating why ~20
@@ -171,7 +250,7 @@ and HTML parsers are written in this repo.
 ## Standards ship as data
 
 2026-08-30, the CommonMark suite 2026-09-05 and ADF's schemas 2026-09-13, the maintainer. Goals 1,
-3 and 7. Valid while each table is fixed data a dependency would only wrap.
+5 and 8. Valid while each table is fixed data a dependency would only wrap.
 
 A table a standard fixes is data rather than a dependency: HTML5's 2125 semicolon-terminated
 character references ship packed in their own module, so entity decoding is complete without one.
@@ -194,7 +273,7 @@ nodes that break it.
 
 ## Any ES2022 engine
 
-2026-09-01, the maintainer. Goal 7. Valid while ES2022 is the floor browsers and servers share.
+2026-09-01, the maintainer. Goal 8. Valid while ES2022 is the floor browsers and servers share.
 
 The library runs on any ES2022 engine, not only Node — a browser as readily as a server. The
 shipped source is ECMAScript and nothing else: no host import, no host global, no DOM.
@@ -208,13 +287,13 @@ never the higher one those repo-only tools want.
 
 ## ESM only
 
-2026-08-23, the maintainer. Goal 7. Valid while the audience's toolchains all import ES modules.
+2026-08-23, the maintainer. Goal 8. Valid while the audience's toolchains all import ES modules.
 
 No CommonJS build, no dual-package hazard.
 
 ## One built entrypoint
 
-2026-08-23, the maintainer. Goal 7. Valid while Node refuses to type-strip under `node_modules`.
+2026-08-23, the maintainer. Goal 8. Valid while Node refuses to type-strip under `node_modules`.
 
 Built JavaScript, `.d.ts` beside it. Do not add a TypeScript-source entrypoint — Node refuses to
 type-strip under `node_modules` (`ERR_UNSUPPORTED_NODE_MODULES_TYPE_STRIPPING`), so it cannot serve
@@ -222,7 +301,7 @@ an npm consumer.
 
 ## Public on npm
 
-2026-08-23, the name 2026-09-01, the maintainer. Goals 2 and 7. Valid while the package's source
+2026-08-23, the name 2026-09-01, the maintainer. Goals 2 and 8. Valid while the package's source
 stays public beside it.
 
 Published to public npm as `@larvit/adf-codec`. Public source: the Gitea repo goes public,
@@ -231,7 +310,7 @@ for the hub rather than the formats around it.
 
 ## The formats are API
 
-2026-08-23, strict input 2026-09-01, content models 2026-09-16, the maintainer. Goals 1 and 6.
+2026-08-23, strict input 2026-09-01, content models 2026-09-16, the maintainer. Goal 1.
 Valid while consumers store what the library emits.
 
 The emitted markdown and HTML are contracts. After 1.0: previously-emitted output parsing
@@ -246,7 +325,7 @@ types in `src/result.ts` hold its shape.
 
 ## The code list
 
-2026-08-25, the maintainer; dated below where a rule came later. Goal 6. Valid while a consumer
+2026-08-25, the maintainer; dated below where a rule came later. Goal 1. Valid while a consumer
 switches on `code` with no `default`.
 
 - Adding, removing or renaming a code is breaking, so a new cause takes an existing code whose
@@ -257,34 +336,35 @@ switches on `code` with no `default`.
   `unsupported-node-shape` — since a code no input reaches is one no consumer can switch on
   (2026-09-20).
 - A refusal no spelling recovers from is a gap in the flavour rather than a code: give the flavour
-  the spelling and the code goes (`unspellable-link`, 2026-09-13). A cause the carry answers gets
+  the spelling and the code goes (`unspellable-link`, 2026-09-13; `unspellable-character` and
-  no code: a mark no spelling writes rides the carry with its node.
+  `unspellable-line-start`, 2026-10-04). A cause the carry answers gets no code: a mark no
+  spelling writes rides the carry with its node.
 
 ## Which code a cause takes
 
-2026-08-28, the maintainer; dated below where a rule came later. Goal 6. Valid while a consumer
+2026-08-28, the maintainer; dated below where a rule came later. Goal 1. Valid while a consumer
 handles one cause alike whichever node, attribute or direction raised it.
 
 - A code names the cause; where one cause recurs across node types, across one mark's attributes
   or across directions, one code covers them all and `path` and `message` say which —
-  `unsupported-nesting-depth` is the 500-level guard whichever direction hits it,
+  `unsupported-nesting-depth` is the 500-level guard whichever direction hits it.
-  `unspellable-character` the text node and the code block alike. Where two codes stay apart, the
+  `unspellable-whitespace` is the newline an inline directive's content slot spells in input; the
-  line between them is what they name: `unspellable-character` is a character CommonMark rewrites
+  emitter carries such a node. A null character in that slot is `unsupported-node-shape`, since
-  wherever text holds it, `unspellable-whitespace` the newline no inline directive's content slot
+  `unspellable-whitespace` does not read true of it (2026-10-04).
-  spans, in either direction.
 - A claim code names the spelling claimed, never the node that spelling would have built: a
   malformed `!adf:table` is a `malformed-directive`, and an alignment colon a
   `malformed-pipe-table` — the flavour's own delimiter row is `-` runs, so the grammar refuses the
   colon rather than ADF's missing column model doing it. What the grammar itself refuses stays a
   claim code, key order among it, and a leaf given a body is refused at its opener, as a container
   missing its closer is (2026-09-16).
-- A directive whose name reads back to no node is `unknown-directive-name` rather than a claim
+- A directive whose name reads back to no node is `unknown-directive-name` rather than a claim code
-  code — the spelling is well formed, and telling that apart from a typo is what a consumer
+  — the spelling is well formed, and telling that apart from a typo is what a consumer switches on
-  switches on when a later MINOR gives the name meaning. A reserved name is a known name, so never
+  when a later MINOR gives the name meaning. A reserved name is a known name, so never that code,
-  that code, and the two the flavour reserves part on form: a form the grammar does not have is a
+  and the names the flavour reserves part on form: a form the grammar does not have is a claim code
-  claim code — `!adf:carry`, whose carry is the fence — and a well-formed form in the wrong place
+  — `!adf:carry`, whose carry is the fence — and a well-formed form in the wrong place is
-  is `unsupported-node-shape`, `!adf:listBreak` parting anything but two adjacent lists of one
+  `unsupported-node-shape`, `!adf:listBreak` parting anything but two adjacent lists of one type,
-  type (2026-09-01).
+  `!adf:textBreak{}` anything but two adjacent text nodes CommonMark would read back as one,
+  `!adf:doc` standing beside another block (2026-09-01, the text break and `doc` 2026-10-03).
 - A well-formed directive the node tables refuse — an attribute a node does not hold or spells
   elsewhere, a value outside its kind or its canonical spelling, an argument, or a body of a shape
   its content model does not take — is `unsupported-node-shape`, the emitter's code for the same
@@ -295,21 +375,21 @@ handles one cause alike whichever node, attribute or direction raised it.
 
 ## `message` and `path`
 
-2026-09-03, the path 2026-09-23, the maintainer. Goals 3 and 6. Valid while a person fixing the
+2026-09-03, the path 2026-09-23, the maintainer. Goals 1 and 5. Valid while a person fixing the
 input reads `message`.
 
 - A message names the violation, not the rule alone — a rule by itself states a truth the reader
   must invert before it reads as a failure — and where the flavour's claim refuses ordinary prose
   it names the escape that unclaims the form claimed: `\!adf:` for a directive, block line and
   inline alike, `\|` for every pipe row.
-- `not-an-adf-document` carries the document's own path throughout: seven of the guard's eight
+- `not-an-adf-document` carries the document's own path throughout: seven of the guard's nine
-  branches read the document's own shape, and threading a path to the eighth — a malformed node
+  branches read the document's own shape, and threading a path to the other two, which look anywhere
-  anywhere in the tree — wants the manual stack §Nothing recurses unbounded forces, whose empty
+  in the tree — a malformed node, or an object holding itself — wants the manual stack §Nothing
-  half no input reaches. The message names the violation instead.
+  recurses unbounded forces. The message names the violation instead.
 
 ## Publish on a version bump
 
-2026-08-23, converging 2026-09-03, the maintainer. Goal 7. Valid while CI on `main` holds the npm
+2026-08-23, converging 2026-09-03, the maintainer. Goal 8. Valid while CI on `main` holds the npm
 token.
 
 `package.json` version on `main` is the source of truth. CI on `main`: tests green and the version
@@ -325,7 +405,7 @@ depend on a store that the gate would then have to keep.
 
 ## Docs describe the release being built
 
-2026-09-16, the maintainer. Goal 7. Valid while a bump on `main` publishes.
+2026-09-16, the maintainer. Goal 8. Valid while a bump on `main` publishes.
 
 Docs on `main` describe the release being built rather than the version npm holds, so they match it
 the moment the bump publishes; add no interim note marking the gap.
@@ -341,7 +421,7 @@ nesting a spelling inside its own kind (`*(*a*)*`) names that mark once.
 
 ## The gate runs on Deno and Bun
 
-2026-09-01, Deno's reason 2026-09-28, the maintainer. Goals 7 and 8. Valid while the library claims
+2026-09-01, Deno's reason 2026-09-28, the maintainer. Goals 4 and 8. Valid while the library claims
 any ES2022 engine.
 
 The gate runs the suite under Deno and Bun as well as Node. Bun runs JavaScriptCore, the one engine
@@ -353,7 +433,7 @@ over the corpus rather than over a smoke import.
 
 ## The gate installs the tarball
 
-2026-09-03, the maintainer. Goal 7. Valid while consumers install the packed package.
+2026-09-03, the maintainer. Goal 8. Valid while consumers install the packed package.
 
 The gate packs the build and installs the tarball under `package-tests/`, so `files`, `exports`
 and `types` are proved on the artifact that ships rather than on the source tree a self-reference
@@ -365,7 +445,7 @@ resolver maps them, under `NodeNext` alone; a `.d.ts` reader that is not `tsc` s
 
 ## Firefox reads the build
 
-2026-09-04, the maintainer. Goal 7. Valid while the library claims a browser and no other leg runs
+2026-09-04, the maintainer. Goal 8. Valid while the library claims a browser and no other leg runs
 SpiderMonkey.
 
 A headless Firefox loads `dist/index.js` over HTTP and converts the round-trip, normalization and
@@ -393,8 +473,8 @@ compared against `undefined` — have a half no valid document reaches.
 
 ## The size ratchet
 
-2026-09-20, the maintainer. Goal 10. Valid while no measure picks out what readers find hard
+2026-09-20, the maintainer. KISS, a technical principle. Valid while no measure picks out what
-better than a function's length.
+readers find hard better than a function's length.
 
 `.oxlintrc.json`'s single rule, over the files `tsconfig.build.json` builds, is a per-function line
 ceiling, set at that set's worst and moving only downward. It covers the built files alone, since
@@ -408,6 +488,26 @@ config gone missing fails the leg instead of falling back to oxlint's own defaul
 `--deny-warnings`, since a rule from a category this config never names arrives as a warning it
 exits 0 on.
 
+## The project ships under the comprehension floor until items 59, 60, 61 and 62 land
+
+2026-10-03, the maintainer. KISS, a technical principle, and its comprehension floor of 7. Valid
+while `todo.md` items 59, 60, 61 and 62 are open.
+
+A four-seat comprehension panel scored the project under the floor of 7. Its scoring run of
+2026-10-04 is the baseline. Since 2026-10-04, a chunk whose panel scores any dimension lower
+improves what the seats named and scores again, and after three such rounds asks the maintainer.
+
+| Seat | Navigation | Locality | Shape | Self-sufficiency | Overall |
+|---|---|---|---|---|---|
+| Junior | 7 | 5.5 | 6.5 | 6 | 6 |
+| Mid | 7 | 5.5 | 6.5 | 6 | 6 |
+| Senior | 7 | 5.5 | 6.5 | 5.5 | 6 |
+| Architect | 7 | 5.5 | 6 | 6 | 6 |
+| Mean | 7.00 | 5.50 | 6.38 | 5.88 | 6.00 |
+
+Three panels on near-identical code scored overall means of 5.88, 5.75 and 5.75, and a seat moves
+±0.5 between runs.
+
 ## Properties on a fixed seed
 
 2026-09-14, the maintainer. Goal 1. Valid while a red gate must reproduce.
@@ -417,15 +517,15 @@ markdown, on a fixed seed in the gate; a counterexample found becomes a round-tr
 
 ## The CommonMark suite checks three ways
 
-2026-08-27, the maintainer. Goals 1 and 8. Valid while the suite's answers are HTML ADF cannot be
+2026-08-27, the maintainer. Goals 1 and 4. Valid while the suite's answers are HTML ADF cannot be
 compared against.
 
 Each example is a named error or markdown that parses and emits to itself byte for byte; its
 reference HTML's text, tags stripped and entities decoded, equals the parsed document's; and its
 elements count the marks and nodes they map to. The fixpoint alone passes a parser returning the
 empty document, the text alone one dropping every emphasis. An exception is the maintainer's to
-add, and valid CommonMark parsing to a document `adfToMarkdown` refuses where a spelling could exist
+add, and valid CommonMark parsing to a document `adfToMarkdown` refuses is a bug to fix, never an
-is a bug to fix, never an exception.
+exception.
 
 ## The flavour spec is read as a source
 
@@ -462,6 +562,15 @@ format, as its parser does. A list giving way to the directive form refuses at z
 than walking again; counting every list twice halved the list limit, counting the directive form
 once doubled the parser's frames per level.
 
+## No value `JSON.parse` or `structuredClone` builds loops a call
+
+2026-10-04, the maintainer. Goals 1 and 9. Valid while every persona hands in plain data, as
+`JSON.parse` or `structuredClone` builds it.
+
+The guards walk a value by `Object.values` and refuse a cycle in it. An inherited or non-enumerable
+key, a getter, a Proxy or a custom iterator is the caller's to rule out: no persona builds one.
+Goal 9's size counts ADF as JSON, so a shared object costs once per place it is held.
+
 ## Nothing spreads an unbounded array
 
 2026-09-18, the maintainer. Goal 1. Valid while engines cap a call's arguments.
@@ -523,7 +632,7 @@ refuses it — which is how the whitespace carry finds a line edge.
 
 ## Emphasis follows CommonMark's matching
 
-2026-08-27, the maintainer. Goals 1 and 8. Valid while CommonMark's emphasis rules are the
+2026-08-27, the maintainer. Goals 1 and 4. Valid while CommonMark's emphasis rules are the
 reader's.
 
 Emphasis is spelled against CommonMark's matching, never flanking alone: a delimiter run in text
@@ -532,7 +641,7 @@ only ones in play, and a pair that matching hands to another delimiter rides the
 
 ## Readable spellings take the `try` prefix
 
-2026-09-21, the maintainer. Goals 1 and 4. Valid while a readable spelling's refusal would cost a
+2026-09-21, the maintainer. Goals 1 and 6. Valid while a readable spelling's refusal would cost a
 document the general form spells.
 
 A readable spelling tried ahead of a general one takes the `try` prefix and fails only where the
@@ -554,8 +663,8 @@ is the markdown flavour's choice, not ADF's.
 
 ## The source parts by ADF and format
 
-2026-08-27, placement 2026-09-18, `adf/`'s bar 2026-09-21, the maintainer. Goal 2. Valid while
+2026-08-27, placement 2026-09-18, `adf/`'s bar 2026-09-21, `plain/` 2026-10-03, the maintainer.
-each format has a reader and a writer through ADF.
+Goal 2. Valid while each format has a reader and a writer through ADF.
 
 `src/adf/` holds ADF's own knowledge, imports no format, and is where a construct both formats read
 lives: the question is answered in ADF's vocabulary — a node type, an attribute kind, a content
@@ -568,13 +677,15 @@ them. A primitive knowing neither ADF nor a format stays at `src/` root. A const
 `spec/flavour.md` draws, and a placement nothing here settles goes beside its only reader, or in
 what both read where there are two.
 
-Each format directory parts into `emit/` (ADF→format) and `parse/` (format→ADF), the rest of it
+A flavour's own code, both directions included, sits in its own directory: `markdown/plain/`;
-holding what both directions read. A construct's reader lives there beside the regex the emitter
+`todo.md` item 62 moves what still sits in `parse/` and `emit/`. Otherwise each format directory
-escapes against, so the two cannot drift; a reader with no emit counterpart goes in `parse/`,
+parts into `emit/` (ADF→format) and `parse/` (format→ADF), the rest of it holding what both
-unless it is part of a construct that side already holds — a grammar stays in one file rather than
+directions read. A construct's reader lives there beside the regex the emitter escapes against, so
-splitting across the seam. A rule both directions must answer alike — whether a list marker
+the two cannot drift; a reader with no emit counterpart goes in `parse/`, unless it is part of a
-interrupts a paragraph — is one function there too, never a copy per direction, however
+construct that side already holds — a grammar stays in one file rather than splitting across the
-conservative the copy would be. Where the rule is the emitter's own choice, input consults it
+seam. A rule both directions must answer alike — whether a list marker interrupts a paragraph — is
-rather than restating it, and that is the only import `parse/` takes from `emit/` —
+one function there too, never a copy per direction, however conservative the copy would be. Where
-`commonMarkSpelling` and `openingLinkTakesDirective` — so no fixture the emitter writes can be
+the rule is the emitter's own choice, input consults it rather than restating it, and that is the
-refused, and a spelling the emitter refuses gives its own error rather than a second name for it.
+only value import `parse/` takes from `emit/` — `commonMarkSpelling` and `openingLinkTakesDirective`
+— so no fixture the emitter writes can be refused, and a spelling the emitter refuses gives its own
+error rather than a second name for it.

spec/flavour.md

@@ -1,12 +1,14 @@
 # The markdown flavour
 
 The grammar of the extended markdown `adfToMarkdown` emits and `markdownToAdf` parses. Plain
-CommonMark is a subset apart from raw HTML (below), with three carve-outs: literal text that matches
+CommonMark is a subset apart from raw HTML (below), with four carve-outs: literal text that matches
-directive syntax below or reads as a pipe table is claimed by the flavour, and a matched `~~` pair
+directive syntax below or reads as a pipe table is claimed by the flavour, a matched `~~` pair
-spells `strike` (escape the `!adf:`, `|` or `~` to keep it literal) — and one gap: a CommonMark
+spells `strike` (escape the `!adf:`, `|` or `~` to keep it literal), and a code fence whose info
-image fits only as its own title-less paragraph — mid-text and titled images are named errors. The
+string opens `adf:` is the opaque carry (drop the info string and wrap the fence in
-emitted form is contract (`docs/decisions.md` §The formats are API). Per-node syntaxes build on this
+`!adf:codeBlock {language="adf:…"}` to keep it code) — and one gap: a CommonMark image fits only as
-grammar in the sections below.
+its own title-less paragraph — mid-text and titled images are named errors. The emitted form is
+contract (`docs/decisions.md` §The formats are API). Per-node syntaxes build on this grammar in the
+sections below.
 
 ## Canonical form
 
@@ -44,7 +46,8 @@ normalizes to it through the round-trip.
   CommonMark admits no spelling — the end of a block, inside an ATX heading — or where the node
   carries an attribute, it is the inline directive.
 - An empty paragraph — real payloads carry them — is an `!adf:paragraph` … `!adf:/paragraph` pair
-  holding nothing.
+  holding nothing, and one whose `content` is an empty array the pair
+  `!adf:paragraph {content=empty}` … `!adf:/paragraph` (Attributes).
 - Links `[text](url)`; `<…>` around a destination containing spaces, `<>` an empty one beside a
   title; title in double quotes. A backslash escapes a parenthesis the destination leaves
   unbalanced, and a quote inside the title; a balanced pair stays bare. `<url>` autolink form only
@@ -67,9 +70,10 @@ normalizes to it through the round-trip.
   matching below, which is what lets the emitter decide its own pairings.
 - Blocks separated by one blank line at document level, inside a blockquote and between CommonMark
   blocks; inside a directive container a pair holding a directive block takes none. No trailing
-  whitespace outside a code
+  whitespace outside a code block's content, single trailing newline. A document whose `content` is
-  block's
+  an empty array is the empty string, and markdown holding no block reads back to it; a document
-  content, single trailing newline; a document with no blocks is the empty string.
+  holding no `content` key is the leaf `!adf:doc {content=none}` as its only block, which is a
+  named error anywhere else or spelled any other way.
 
 ## Directives
 
@@ -81,9 +85,11 @@ result naming it at the opener, whatever follows it — so output an old emitter
 escaped, and erroring input gaining meaning later is MINOR, never a reparse (`docs/decisions.md`
 §The formats are API). Each name belongs to one position, and a name the other one spells — a mark
 or an inline node written as a block directive, a block node written inline — is a different error,
-naming the spelling it takes. Two reserved names read back to no node: `carry` for the opaque carry,
+naming the spelling it takes. Four reserved names read back to no node: `carry` for the inline
-as both directive name and fence info string, and `listBreak` for the leaf that parts two adjacent
+opaque carry, `listBreak` for the leaf that parts two adjacent lists and `doc` for a document
-lists (Canonical form).
+holding no `content` key (Canonical form), and `textBreak` for the leaf that parts two text nodes
+(Inline nodes). Every fence info string opening `adf:` is reserved for the block carry (The opaque
+carry).
 
 **Claiming**: an unescaped `!adf:` claims wherever it stands. What follows picks the form: `/name`
 closes a container, and a name picks by what follows it in turn — a space or the line's end a block
@@ -144,6 +150,13 @@ ends the name (`!adf:hardBreak{}`). Input reads that spelling alone: keys out of
 quoted where bare carries it, an escape longer than it need be, an empty `{attrs}` on a block line
 or after a `[content]`, and a number or `json` value outside its canonical JSON spelling are each a
 named error naming the spelling to write instead.
+`attrs`, `content` and `marks` are reserved keys on every directive — block, inline node and mark —
+whose bare value `empty` spells the node's or mark's key holding an empty object or array:
+`!adf:underline[a]{attrs=empty}`, `!adf:date{content=empty}`, `!adf:hardBreak{marks=empty}`. A
+container spelling `content=empty` closes with no body; `attrs=empty` stands beside no other
+attribute, argument or content slot; and an inline node spelling `marks=empty` stands inside no
+mark spelling. Any other value of a reserved key is a named error, except on a block's `marks`
+(Block nodes).
 
 **Escaping**: the emitter backslash-escapes whatever literal text would otherwise parse as
 directive syntax — every literal `!adf:`, `]` inside content, a bracket a link's destination and
@@ -165,21 +178,25 @@ and restores to a deep-equal node. A carry may hold a node the emitter spells na
 unreinterpreted, and the next emit spells it canonically (`docs/decisions.md` §The round-trip is the
 product). Block and inline positions canonicalize differently, each fitting where it sits:
 
-- **Block position**: a fenced code block with info string `carry`, body = the node's JSON —
+- **Block position**: a fenced code block with info string `adf:` and the node's type, body = the
-  two-space indent, object keys sorted.
+  node's JSON without its `type` — two-space indent, object keys sorted: ```` ```adf:blockCard ````.
+  A type no info string carries back, by the rule a `codeBlock`'s language follows, leaves the info
+  string `adf:` and keeps `type` in the body. A body holding `type` under a named type, or a fence
+  whose info string is `adf:` alone while its body's `type` could be spelled in the info string, is
+  a named error.
 - **Inline position**: `!adf:carry{json="…"}` — compact serialization (keys sorted, no whitespace),
   JSON-string-escaped into the attribute.
 
-The info string `carry` is reserved: a genuine `codeBlock` whose `language` is exactly `carry` takes
+Every info string opening `adf:` is reserved: a genuine `codeBlock` whose `language` opens so takes
 the attribute the section below keeps for a language no info string holds, so the reservation
-stays absolute.
+stays absolute. In block-directive position `!adf:carry` is a named error — the carry's block form
-In block-directive position `!adf:carry` is a named error — the carry's block form is the fence.
+is the fence.
 
 ## Raw HTML in input
 
 CommonMark input may contain raw HTML. `markdownToAdf` routes each construct through the foreign
 HTML element mapping (`docs/decisions.md` §Foreign HTML sorts three ways; specified with the HTML
-dialect, todo.md milestone 6) — ADF has no raw-HTML node, so a construct without a mapping, comments
+dialect, `todo.md` item 6) — ADF has no raw-HTML node, so a construct without a mapping, comments
 and processing instructions included, is an error result naming it. The flavour never emits raw
 HTML.
 
@@ -195,13 +212,14 @@ Each section lists attributes as `name (type)`. A parenthesized value set docume
 payloads hold; the type stays string and any value round-trips verbatim. Values map to attrs by
 type: strings verbatim, numbers and booleans in canonical JSON spelling — quoted where not bare
 (`width="33.33"`) — and `json` values as the inline carry's serialization (compact, keys sorted),
-quoted. `markdownToAdf` emits `attrs`, `content` and `marks` keys only when non-empty; editor-normal
+quoted, `-0` spelled `-0`. `markdownToAdf` builds an `attrs`, `content` or `marks` key only where the
-ADF reads an empty attrs object, marks array or content array as the absent key (`docs/decisions.md`
+markdown spells one, an empty one through its reserved key (Attributes), so a document reads back
-§Equality is editor-normal) — the grammar's empty-`{attrs}` omission already collapses the two
+deep-equal (`docs/decisions.md` §Equality is deep). A node CommonMark spells takes the directive
-spellings.
+form to hold an empty key.
 
 Marks on a block node ride the reserved attribute key `marks` — the node's marks array as a
-`json` value: `!adf:layoutSection {marks="[{\"attrs\":{\"mode\":\"wide\"},\"type\":\"breakout\"}]"}`.
+`json` value, `marks=empty` where it is empty:
+`!adf:layoutSection {marks="[{\"attrs\":{\"mode\":\"wide\"},\"type\":\"breakout\"}]"}`.
 A section saying its body is inline takes at most one paragraph, whose inline content becomes
 the node's `content`; any other body is a named error, and an empty pair is a node holding none.
 
@@ -217,20 +235,24 @@ cannot — `localId` (string) on any of them, marks, and the values below — ta
 form.
 
 - `blockquote`, `bulletList`, `listItem` — containers, block body. Attributes: `localId` (string).
-- `codeBlock` — container, body one fenced code block whose info string is the language and whose
+- `codeBlock` — container, body one fenced code block per text node, each fence's info string the
-  content is the node's. Attributes: `hideLineNumbers` (boolean), `language` (string), `localId`
+  language and its content the node's text; a node holding no `content` key is one empty fence.
-  (string), `uniqueId` (string), `wrap` (boolean). A language no info string carries back — empty,
+  Attributes: `hideLineNumbers` (boolean), `language` (string), `localId` (string), `uniqueId`
-  the reserved `carry`, or holding a backtick, a backslash, a control character, edge whitespace or
+  (string), `wrap` (boolean). A language no info string carries back — empty, opening the reserved
-  an entity reference — rides the `language` attribute instead and the fence carries no info
+  `adf:`, or holding a backtick, a backslash, a control character, edge whitespace or an entity
-  string; writing it in the slot that rule leaves empty, or in both, is a named error. The body is
+  reference — rides the `language` attribute instead and the fences carry no info string, and so
-  one ordinary code block, and a fence's info string decodes escapes and entity references as any
+  does a language beside `content=empty`, which has no fence; writing it in the slot that rule
-  other does.
+  leaves empty, or in both, is a named error, and so are fences whose info strings differ and an
+  empty fence beside another. Each fence is an ordinary code block, and its info string decodes
+  escapes and entity references as any other does. A node holding a child no fence holds — any but
+  a text node holding text free of carriage returns and null characters, and carrying no marks,
+  `attrs` or `content` — rides the block carry.
 - `heading` — container, inline body. Attributes: `level` (number), `localId` (string). `level` is
   the `#` count, so a heading carrying none, or one that is no whole number from 1 to 6, has no
   CommonMark spelling.
 - `orderedList` — container of `listItem`, block body. Attributes: `localId` (string), `order`
-  (number). `order` is the first marker, so a list carrying none, one that is no whole number
+  (number). `order` is the first marker, so a list carrying none, one that is `-0` or no whole
-  from 0, or one whose markers would run past 999999999, has no CommonMark spelling.
+  number from 0, or one whose markers would run past 999999999, has no CommonMark spelling.
 - `paragraph` — container, inline body. Attributes: `localId` (string).
 - `rule` — leaf. Attributes: `color` (string, `#rrggbb`), `localId` (string), `style` (`dashed`
   `dotted` `fade` `sketch` `solid`), `weight` (number, 1–3).
@@ -426,10 +448,11 @@ Right.
 Attributes and the carry fallback read as in the block sections, the carry in its inline form. Of
 the nodes below, `emoji`, `mention` and `status` spell their `text` attribute in the content slot as
 plain text: `[]` is the empty string, absent content is the absent attribute, non-empty content
-parsing to anything but one text node carrying neither marks, attributes nor content — adjacent text
+parsing to anything but one text node carrying neither marks, attributes nor content is a named
-nodes with identical marks and no attributes merged first — is a named error, and so is a `text` key
+error, and so is a `text` key in `{attrs}`. An enclosing mark spelling does not reach into the slot.
-in `{attrs}`. An enclosing mark spelling does not reach into the slot. The rest take no content,
+An `emoji`, `mention` or `status` whose `text` attribute holds a line ending or a null character
-`!adf:text` included; content on a node that takes none is a named error.
+rides the inline carry; a content slot spelling one is a named error.
+The rest take no content, `!adf:text` included; content on a node that takes none is a named error.
 
 - `date` — Attributes: `localId` (string), `timestamp` (string, epoch milliseconds).
 - `emoji` — Attributes: `id` (string), `localId` (string), `shortName` (string, `:name:`), `text`
@@ -451,20 +474,32 @@ in `{attrs}`. An enclosing mark spelling does not reach into the slot. The rest
 Shipped !adf:emoji[🎉]{shortName=":tada:"} on !adf:date{timestamp=1756080000000}.
 ```
 
-**Whitespace CommonMark cannot hold.** A newline inside a text node, and a space or tab where
+**Text CommonMark cannot hold plainly.** A carriage return in text is `&#13;`, which CommonMark
-CommonMark strips or refuses one — a block's inline content edges, either side of a line break, an
+reads back as the character. Three things are spelled `!adf:text{text="…"}`: a newline inside a text
-em, strong or strike spelling's inner edges, a pipe cell's edges — is spelled `!adf:text{text="…"}`,
+node; a null character, which CommonMark reads as U+FFFD; and a space or tab where CommonMark strips
-the reserved key carrying the node's text, escaped by the attribute grammar and never literal: pipe
+or refuses one — a block's inline content edges, either side of a line break, an em, strong or
-cells trim and pad. The emitter wraps the whitespace run alone and leaves the rest plain text;
+strike spelling's inner edges, a pipe cell's edges. The reserved key carries the node's text,
-`markdownToAdf` merges adjacent text nodes carrying identical marks and no attributes
+escaped by the attribute grammar and never literal: pipe cells trim and pad. The emitter wraps the
-(`docs/decisions.md` §Equality is editor-normal). Input reads that spelling alone: the value is one
+run alone and leaves the rest plain text, which the spelled run joins on reading. Input reads that
-run of spaces and tabs, or one run of newlines, and anything else — a mixed run, or text CommonMark
+spelling alone: the value is one run of spaces and tabs, one run of newlines, or one run of null
-carries plainly — is a named error.
+characters, and anything else — a mixed run, or text CommonMark carries plainly — is a named error.
 
 ```
 !adf:text{text="  "}Two leading spaces held, and one text node split!adf:text{text="\n"}over two lines.
 ```
 
+**Adjacent text nodes.** CommonMark reads two adjacent text nodes back as one where neither is
+carried, neither holds `attrs` or an empty key, and their marks are identical, attributes included.
+The reserved leaf `!adf:textBreak{}` parts such a pair, inside every mark spelling the two share; a
+code span holds no directive, so it closes and reopens. It builds no node and reads only between
+two such nodes: elsewhere, or with `[content]` or `{attrs}`, it is a named error (`docs/decisions.md`
+§`!adf:textBreak{}` parts text CommonMark would join). A text node holding `attrs`, `content` or an
+empty key, or holding no text, rides the inline carry.
+
+```
+Hello, !adf:textBreak{}world — **Hello, !adf:textBreak{}world** — `a`!adf:textBreak{}`b`
+```
+
 ## Marks
 
 An inline node's marks ride the spelling wrapped around them, never the block sections' reserved
@@ -492,20 +527,21 @@ the directive form, open to no literal reading, is a named error.
 A spelling adds its mark to every inline node it wraps, and nesting is the marks array in order,
 outermost first: `_!adf:underline[x]_` gives marks `[em, underline]`, `!adf:underline[_x_]` the
 reverse. `adfToMarkdown` nests in the order the array holds rather than sorting it —
-`docs/decisions.md` §Equality is editor-normal restores the array, not a set — and opens each
+`docs/decisions.md` §Equality is deep restores the array, not a set — and opens each spelling once
-spelling once over the longest run of adjacent inline nodes carrying an identical mark, attributes
+over the longest run of adjacent inline nodes carrying an identical mark, attributes included, at
-included, at that depth. A run breaks at every node the emitter carries, so no emitted carry sits
+that depth: `attrs: {}` differs from no `attrs`, and a directive spells it `{attrs=empty}`. A run
-inside a mark spelling.
+breaks at every node the emitter carries, so no emitted carry sits inside a mark spelling.
 
 An inline node whose marks no nesting spells — a mark type not listed here, an attrs key its
-spelling does not list, a value that is not the spelling's type, an attribute the spelling needs
+spelling does not list, a value that is not the spelling's type, an attribute the spelling needs and
-and the mark lacks, an order putting a code span outside another mark, `code` over anything but a
+the mark lacks, an empty `attrs` on a mark CommonMark spells, an order putting a code span outside
-text node or over text holding a newline, or a spelling CommonMark's flanking rules cannot open or
+another mark, `code` over anything but a text node holding text, or over text holding a line ending
-close where the run sits (`un**-real**istic`), or one CommonMark's matching pairs elsewhere — the
+or a null character, or a spelling CommonMark's flanking rules cannot open or close where the run
-intra-word `*` runs together with a neighbouring `**`, and the multiple-of-3 rule can leave the
+sits (`un**-real**istic`), or one CommonMark's matching pairs elsewhere — the intra-word `*` runs
-merged run's pairing to another delimiter — rides the inline carry whole. An opaque carry inside a
+together with a neighbouring `**`, and the multiple-of-3 rule can leave the merged run's pairing to
-mark spelling is a named error in input: the carry restores its node exactly, marks included
+another delimiter — rides the inline carry whole. An opaque carry inside a mark spelling is a named
-(`docs/decisions.md` §Unknown nodes ride the carry).
+error in input: the carry restores its node exactly, marks included (`docs/decisions.md` §Unknown
+nodes ride the carry).
 
 ```
 !adf:textColor[**Overdue**]{color="#ae2e24"}, H!adf:subsup[2]{type=sub}O, !adf:underline[signed].

src/adf/document.test.ts

@@ -82,3 +82,23 @@ test("reads a node's siblings as a walk rather than as one call's arguments", ()
   assert.equal(isAdfDocument(wide), true)
   assert.equal(fault(wide), 'accepted')
 })
+
+test('refuses an object holding itself, and accepts one shared', () => {
+  const holdsItself = 'an ADF document is a tree: an object in it holds itself'
+  const paragraph: { content: unknown[]; type: string } = { content: [], type: 'paragraph' }
+  paragraph.content.push(paragraph)
+  assert.equal(fault({ content: [paragraph], type: 'doc', version: 1 }), holdsItself)
+  const document: { content: unknown[]; type: string; version: number } = { content: [], type: 'doc', version: 1 }
+  document.content.push(document)
+  assert.equal(fault(document), holdsItself)
+  const attrs: Record<string, unknown> = {}
+  attrs['a'] = [attrs]
+  assert.equal(fault({ content: [{ attrs, type: 'paragraph' }], type: 'doc', version: 1 }), holdsItself)
+  assert.equal(fault({ content: [{ marks: [{ attrs, type: 'link' }], text: 'x', type: 'text' }], type: 'doc', version: 1 }), holdsItself)
+  assert.equal(isAdfDocument({ content: [{ attrs, type: 'paragraph' }], type: 'doc', version: 1 }), false)
+  const bold = { type: 'strong' }
+  const text = { marks: [bold], text: 'x', type: 'text' }
+  const shared = { content: [text, text], type: 'paragraph' }
+  const values = { b: 1 }
+  assert.equal(fault({ content: [shared, shared, { attrs: { a: [values, values] }, type: 'paragraph' }], type: 'doc', version: 1 }), 'accepted')
+})

src/adf/document.ts

@@ -1,6 +1,7 @@
 import type { ConvertFault } from '../result.ts'
 import { isJsonValue, overNested, type JsonValue } from '../json-value.ts'
 import { largestNesting } from '../nesting.ts'
+import { serializeCanonicalJson } from '../canonical-json.ts'
 
 export type AdfAttributes = { [key: string]: JsonValue }
 
@@ -17,6 +18,8 @@ export type AdfNode = {
   type: string
 }
 
+export type EmptyKey = 'attrs' | 'content' | 'marks'
+
 export type AdfDocument = {
   content?: AdfNode[]
   type: 'doc'
@@ -40,6 +43,7 @@ export function adfDocumentFault(value: unknown): ConvertFault | undefined {
   const held: unknown = value['content']
   if (!Array.isArray(held)) return notADocument(`an ADF document's content is an array: found ${describe(held)}`)
   const content: readonly unknown[] = held
+  if (holdsItself(content)) return notADocument('an ADF document is a tree: an object in it holds itself')
   if (!isNodeArray(content)) return notADocument("an ADF document's content holds ADF nodes: one of them is not")
   return nestingFault(content)
 }
@@ -48,11 +52,49 @@ export function attributeNestingMessage(key: string, type: string): string {
   return `the ${key} attribute of ${type} nests deeper than the ${largestNesting} levels an attribute carries`
 }
 
-export function carriesOnly(node: AdfNode, attributes: readonly string[]): boolean {
+export function holdsOnlyAttributes(node: AdfNode, attributes: readonly string[]): boolean {
-  if (nodeMarks(node).length > 0 || node.text !== undefined) return false
+  if (nodeMarks(node).length > 0 || node.text !== undefined || emptyKeys(node).length > 0) return false
   return holdsOnly(nodeAttrs(node), attributes)
 }
 
+export function emptyKeys(held: { attrs?: AdfAttributes; content?: AdfNode[]; marks?: AdfMark[] }): EmptyKey[] {
+  const keys: EmptyKey[] = []
+  if (held.attrs !== undefined && Object.keys(held.attrs).length === 0) keys.push('attrs')
+  if (held.content?.length === 0) keys.push('content')
+  if (held.marks?.length === 0) keys.push('marks')
+  return keys
+}
+
+// No attrs, content or empty marks; a format may spell this node as text, and anything more rides a carry.
+export function isBareText(node: AdfNode): boolean {
+  return node.type === 'text' && node.attrs === undefined && node.content === undefined && node.marks?.length !== 0
+}
+
+export function isUnmarkedBareText(node: AdfNode): boolean {
+  return isBareText(node) && node.marks === undefined
+}
+
+export function identicalMark(left: AdfMark, right: AdfMark): boolean {
+  return marksKey([left]) === marksKey([right])
+}
+
+export function identicalMarks(left: readonly AdfMark[], right: readonly AdfMark[]): boolean {
+  return marksKey(left) === marksKey(right)
+}
+
+export function mergeAdjacentText(nodes: readonly AdfNode[], joins: (previous: AdfNode, node: AdfNode) => boolean): AdfNode[] {
+  const merged: AdfNode[] = []
+  for (const node of nodes) {
+    const previous = merged[merged.length - 1]
+    if (previous !== undefined && joins(previous, node)) {
+      merged[merged.length - 1] = { ...previous, text: `${previous.text ?? ''}${node.text ?? ''}` }
+      continue
+    }
+    merged.push(node)
+  }
+  return merged
+}
+
 // Depth is the walks' business, not the shape's: the guard waves a deep document through as blocks and marks do.
 export function isAdfDocument(value: unknown): value is AdfDocument {
   const fault = adfDocumentFault(value)
@@ -81,6 +123,23 @@ export function nodeMarks(node: { marks?: AdfMark[] }): readonly AdfMark[] {
   return node.marks ?? []
 }
 
+// Tracks ancestors alone: a tree may share an object, but an object holding itself walks the guards forever.
+function holdsItself(root: object): boolean {
+  const pending = [{ depth: 0, item: root }]
+  const ancestors: object[] = []
+  const onPath = new Set<unknown>()
+  while (pending.length > 0) {
+    const entry = pending.pop()
+    if (entry === undefined) continue
+    while (ancestors.length > entry.depth) onPath.delete(ancestors.pop())
+    if (onPath.has(entry.item)) return true
+    ancestors.push(entry.item)
+    onPath.add(entry.item)
+    for (const child of Object.values(entry.item)) if (typeof child === 'object' && child !== null) pending.push({ depth: entry.depth + 1, item: child })
+  }
+  return false
+}
+
 function isNodeArray(value: readonly unknown[]): value is readonly AdfNode[] {
   const pending: unknown[] = [...value]
   while (pending.length > 0) {
@@ -99,6 +158,13 @@ function isNodeArray(value: readonly unknown[]): value is readonly AdfNode[] {
   return true
 }
 
+function marksKey(marks: readonly AdfMark[]): string {
+  return serializeCanonicalJson(
+    marks.map((mark) => (mark.attrs === undefined ? [mark.type] : [mark.type, mark.attrs])),
+    'compact',
+  )
+}
+
 function nestingFault(nodes: readonly AdfNode[]): ConvertFault | undefined {
   const pending: AdfNode[] = [...nodes]
   while (pending.length > 0) {

src/canonical-json.ts

@@ -18,7 +18,7 @@ export function serializeCanonicalJson(value: JsonValue, spelling: JsonSpelling)
     const { depth, value: held } = next
     if (Array.isArray(held)) schedule(pending, '[', held.map((item) => ({ label: '', value: item })), ']', indent, depth)
     else if (held !== null && typeof held === 'object') schedule(pending, '{', objectMembers(held, indent), '}', indent, depth)
-    else text.push(JSON.stringify(held))
+    else text.push(Object.is(held, -0) ? '-0' : JSON.stringify(held))
   }
   return text.join('')
 }

src/conformance/adf-property.test.ts

@@ -2,12 +2,13 @@ import assert from 'node:assert/strict'
 import fc from 'fast-check'
 import test from 'node:test'
 
+import type { AdfNode } from '../adf/document.ts'
 import { adfDocument, propertyRuns, propertyTimeout } from './property-harness.ts'
 import { adfToMarkdown } from '../markdown/emit/adf-to-markdown.ts'
-import { adfToPlainMarkdown } from '../markdown/emit/plain-reduction.ts'
+import { adfToPlainMarkdown, reduceToPlain } from '../markdown/plain/adf-to-plain-markdown.ts'
 import { directivePrefix } from '../markdown/directive-syntax.ts'
 import { markdownToAdf, plainMarkdownToAdf } from '../markdown/parse/markdown-to-adf.ts'
-import { toEditorNormal } from '../adf/editor-normal.ts'
+import { toEditorNormal } from '../markdown/plain/editor-normal.ts'
 
 const gateRuns = 1600
 const renamedPrefix = '!adg:'
@@ -19,20 +20,34 @@ function readsNoDirective(markdown: string): boolean {
   return read.ok && renamed.ok && JSON.stringify(read.value).replaceAll(directivePrefix, renamedPrefix) === JSON.stringify(renamed.value)
 }
 
-test('a generated document refuses to emit, or its markdown reads back to it', { timeout: propertyTimeout }, () => {
+// Each block's text, an expand's title and an image's alt and url, in document order: what the plain pair keeps.
+function shownText(nodes: readonly AdfNode[]): string[] {
+  const shown: string[] = []
+  for (const node of nodes) {
+    const attrs = node.attrs ?? {}
+    if ((node.type === 'expand' || node.type === 'nestedExpand') && typeof attrs['title'] === 'string') shown.push(attrs['title'])
+    if (node.type === 'media') shown.push(`${JSON.stringify(attrs['alt'] ?? '')} ${JSON.stringify(attrs['url'])}`)
+    const content = node.content ?? []
+    if (content.some((child) => child.type === 'text' || child.type === 'hardBreak')) shown.push(content.map((child) => child.text ?? '\n').join(''))
+    else for (const text of shownText(content)) shown.push(text)
+  }
+  return shown.filter((text) => text !== '')
+}
+
+test('a generated document emits markdown that reads back to it', { timeout: propertyTimeout }, () => {
   fc.assert(
     fc.property(adfDocument, (document) => {
       const emitted = adfToMarkdown(document)
-      if (!emitted.ok) return
+      assert.ok(emitted.ok, emitted.ok ? '' : `${emitted.error.code}: ${emitted.error.message}`)
       const read = markdownToAdf(emitted.value)
       assert.ok(read.ok, read.ok ? '' : `${read.error.code}: ${read.error.message} — reading ${JSON.stringify(emitted.value)}`)
-      assert.deepEqual(toEditorNormal(read.value), document, `reading ${JSON.stringify(emitted.value)}`)
+      assert.deepEqual(read.value, document, `reading ${JSON.stringify(emitted.value)}`)
     }),
     propertyRuns(gateRuns),
   )
 })
 
-test('a generated document writes plain markdown refusing only what the guard refuses, and that markdown reads back to itself', { timeout: propertyTimeout }, () => {
+test('a generated document writes plain markdown refusing only what the guard refuses, and that markdown reads back to its text and to itself', { timeout: propertyTimeout }, () => {
   fc.assert(
     fc.property(adfDocument, (document) => {
       const written = adfToPlainMarkdown(document)
@@ -40,8 +55,19 @@ test('a generated document writes plain markdown refusing only what the guard re
       assert.ok(readsNoDirective(written.value), `a directive in ${JSON.stringify(written.value)}`)
       const read = plainMarkdownToAdf(written.value)
       assert.ok(read.ok, read.ok ? '' : `${read.error.code}: ${read.error.message} — reading ${JSON.stringify(written.value)}`)
+      const reduced = reduceToPlain(document)
+      assert.deepEqual(shownText(read.value.content ?? []), reduced.ok ? shownText(reduced.value.content ?? []) : reduced, `reading ${JSON.stringify(written.value)}`)
       assert.deepEqual(adfToPlainMarkdown(read.value), written, `reading ${JSON.stringify(written.value)}`)
     }),
     propertyRuns(gateRuns),
   )
 })
+
+test('a generated document writes the plain markdown its editor-normal form writes', { timeout: propertyTimeout }, () => {
+  fc.assert(
+    fc.property(adfDocument, (document) => {
+      assert.deepEqual(adfToPlainMarkdown(document), adfToPlainMarkdown(toEditorNormal(document)))
+    }),
+    propertyRuns(gateRuns),
+  )
+})

src/conformance/commonmark-spec.test.ts

@@ -13,7 +13,7 @@ const root = join(dirname(fileURLToPath(import.meta.url)), '..', '..', 'corpus',
 const checks = ['count', 'fixpoint', 'text'] as const
 
 type Check = (typeof checks)[number]
-type ExceptionKind = 'mark-model' | 'pending' | 'unspellable'
+type ExceptionKind = 'mark-model' | 'pending'
 
 type SpecExample = { example: number; html: string; markdown: string; section: string }
 
@@ -30,7 +30,7 @@ function isCheck(value: unknown): value is Check {
 }
 
 function isKind(value: unknown): value is ExceptionKind {
-  return value === 'mark-model' || value === 'pending' || value === 'unspellable'
+  return value === 'mark-model' || value === 'pending'
 }
 
 function isSpecExample(value: unknown): value is SpecExample {
@@ -77,12 +77,12 @@ test('the CommonMark spec suite is 0.31.2, vendored byte-exact', () => {
   assert.equal(digest, 'd431b29d97b6f73e69d547109cf5081578fac931e72afe95639ebe766c1b2a20')
 })
 
-test('every exception is unique, names a parsing example, and files a fixpoint only as unspellable', () => {
+test('every exception is unique, names a parsing example, and files no fixpoint divergence', () => {
   assert.equal(exceptionIndex.size, exceptions.length, 'one exception repeats an example and check another holds')
   for (const entry of exceptions) {
     assert.ok(spec.some((candidate) => candidate.example === entry.example), `exception ${entry.example} names no example in the suite`)
     assert.equal(exampleToRefusal.get(entry.example), undefined, `exception ${entry.example} is on the refusal list, not an exception`)
-    if (entry.check === 'fixpoint') assert.equal(entry.kind, 'unspellable', `exception ${entry.example} files a fixpoint divergence as ${entry.kind}; a fixable hole is given the spelling instead`)
+    assert.notEqual(entry.check, 'fixpoint', `exception ${entry.example} files a fixpoint divergence; the emitter spells every document the parser builds`)
   }
 })
 

src/conformance/corpus.test.ts

@@ -9,7 +9,6 @@ import { isAdfDocument } from '../adf/document.ts'
 import { isJsonValue } from '../json-value.ts'
 import { markdownToAdf } from '../markdown/parse/markdown-to-adf.ts'
 import { serializeCanonicalJson } from '../canonical-json.ts'
-import { toEditorNormal } from '../adf/editor-normal.ts'
 
 const corpusRoot = join(dirname(fileURLToPath(import.meta.url)), '..', '..', 'corpus')
 const errorsRoot = join(corpusRoot, 'errors')
@@ -97,7 +96,7 @@ for (const directory of roundTripDirectories) {
       assert.ok(isAdfDocument(expected), `${name}.json is not an ADF document`)
       const result = markdownToAdf(readFileSync(join(roundTripRoot, directory, `${name}.md`), 'utf8'))
       assert.ok(result.ok, result.ok ? '' : `${result.error.code}: ${result.error.message}`)
-      assert.deepEqual(toEditorNormal(result.value), expected)
+      assert.deepEqual(result.value, expected)
     })
   }
 }
@@ -125,12 +124,12 @@ for (const name of pairedNames(normalizationRoot, '.md', '.json')) {
     assert.ok(isAdfDocument(expected), `${name}.json is not an ADF document`)
     const result = markdownToAdf(readFileSync(join(normalizationRoot, `${name}.md`), 'utf8'))
     assert.ok(result.ok, result.ok ? '' : `${result.error.code}: ${result.error.message}`)
-    assert.deepEqual(toEditorNormal(result.value), expected)
+    assert.deepEqual(result.value, expected)
     const emitted = adfToMarkdown(result.value)
     assert.ok(emitted.ok, emitted.ok ? '' : `${emitted.error.code}: ${emitted.error.message}`)
     const again = markdownToAdf(emitted.value)
     assert.ok(again.ok, again.ok ? '' : `${again.error.code}: ${again.error.message}`)
-    assert.deepEqual(toEditorNormal(again.value), expected)
+    assert.deepEqual(again.value, expected)
   })
 }
 
@@ -146,7 +145,7 @@ for (const name of names(realPayloadsRoot, '.json')) {
     assert.ok(emitted.ok, emitted.ok ? '' : `${emitted.error.code}: ${emitted.error.message}`)
     const parsed = markdownToAdf(emitted.value)
     assert.ok(parsed.ok, parsed.ok ? '' : `${parsed.error.code}: ${parsed.error.message}`)
-    assert.deepEqual(toEditorNormal(parsed.value), payload)
+    assert.deepEqual(parsed.value, payload)
   })
 }
 

src/conformance/markdown-property.test.ts

@@ -31,7 +31,6 @@ import { markdownToAdf } from '../markdown/parse/markdown-to-adf.ts'
 import { nodeContent, nodeMarks } from '../adf/document.ts'
 import { serializeCanonicalJson } from '../canonical-json.ts'
 import { textDirectiveName } from '../markdown/text-directive.ts'
-import { toEditorNormal } from '../adf/editor-normal.ts'
 import { vocabularyPairs } from '../adf/attribute-vocabulary.ts'
 
 type Choice = { arbitrary: Arbitrary<string>; hostile?: true; weight: number }
@@ -419,7 +418,7 @@ function holdsDirectiveShape(document: AdfDocument): boolean {
   return false
 }
 
-test('generated markdown refuses, or what it parses to refuses to emit, or its spelling reads back and spells itself', { timeout: propertyTimeout }, () => {
+test('generated markdown refuses, or its spelling reads back and spells itself', { timeout: propertyTimeout }, () => {
   const parameters = propertyRuns(gateRuns)
   let directiveShaped = 0
   let fixpoints = 0
@@ -428,12 +427,12 @@ test('generated markdown refuses, or what it parses to refuses to emit, or its s
       const parsed = markdownToAdf(input)
       if (!parsed.ok) return
       const emitted = adfToMarkdown(parsed.value)
-      if (!emitted.ok) return
+      assert.ok(emitted.ok, emitted.ok ? '' : `${emitted.error.code}: ${emitted.error.message} — spelling ${JSON.stringify(input)}`)
       fixpoints += 1
       if (holdsDirectiveShape(parsed.value)) directiveShaped += 1
       const read = markdownToAdf(emitted.value)
       assert.ok(read.ok, read.ok ? '' : `${read.error.code}: ${read.error.message} — reading ${JSON.stringify(emitted.value)}`)
-      assert.deepEqual(toEditorNormal(read.value), toEditorNormal(parsed.value), `reading ${JSON.stringify(emitted.value)}`)
+      assert.deepEqual(read.value, parsed.value, `reading ${JSON.stringify(emitted.value)}`)
       const respelled = adfToMarkdown(read.value)
       assert.ok(respelled.ok, respelled.ok ? '' : `${respelled.error.code}: ${respelled.error.message} — spelling ${JSON.stringify(emitted.value)} again`)
       assert.equal(respelled.value, emitted.value)

src/conformance/property-harness.ts

@@ -2,16 +2,17 @@ import assert from 'node:assert/strict'
 import { env } from 'node:process'
 import fc from 'fast-check'
 
-import type { AdfAttributes, AdfDocument, AdfMark, AdfNode } from '../adf/document.ts'
+import type { AdfAttributes, AdfDocument, AdfMark, AdfNode, EmptyKey } from '../adf/document.ts'
 import type { Arbitrary } from 'fast-check'
 import type { AttributeKind, AttributeVocabulary } from '../adf/attribute-vocabulary.ts'
 import type { JsonValue } from '../json-value.ts'
 import { blockArgument } from '../markdown/block-directive.ts'
 import { blockNodes } from '../adf/block-nodes.ts'
 import { directivePrefix } from '../markdown/directive-syntax.ts'
+import { emptyKeys, mergeAdjacentText } from '../adf/document.ts'
 import { inlineNodes } from '../adf/inline-nodes.ts'
+import { joinsWhenRead } from '../markdown/adjacent-text.ts'
 import { markAttributes } from '../adf/mark-attributes.ts'
-import { toEditorNormal } from '../adf/editor-normal.ts'
 
 type Positions = { block: AdfNode; inline: AdfNode }
 
@@ -23,7 +24,7 @@ export const propertyTimeout = 600000
 const depthIdentifier = fc.createDepthIdentifier()
 const emptyCell: AdfNode = { content: [{ type: 'paragraph' }], type: 'tableCell' }
 const flatCommonMarkShapeWeight = 4
-export const markdownPieces = fc.constantFrom(...'aZ09 \t\n!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~é\xa0🎉', 'ab:', 'http://', directivePrefix, `${directivePrefix}a[`, `${directivePrefix}a{`)
+export const markdownPieces = fc.constantFrom(...'aZ09 \t\n\r\0!"#$%&\'()*+,-./:;<=>?@[\\]^_`{|}~é\xa0🎉日ー한𠀀', '==', '[!NOTE]', '[x]', 'ab:', 'http://', directivePrefix, `${directivePrefix}a[`, `${directivePrefix}a{`)
 const nestingCommonMarkShapeWeight = 21
 const spelledTypes = new Set(['text', ...Object.keys(blockNodes), ...Object.keys(inlineNodes), ...Object.keys(markAttributes)])
 
@@ -36,7 +37,11 @@ export function textOf(minLength: number): Arbitrary<string> {
 
 const text = textOf(1)
 const unknownType = fc.oneof(fc.stringMatching(/^[a-z][A-Za-z0-9]{0,7}$/), text).filter((type) => !spelledTypes.has(type))
-const numberValue = fc.oneof({ arbitrary: fc.integer({ max: 10, min: -1 }), weight: 3 }, { arbitrary: fc.double({ noDefaultInfinity: true, noNaN: true }), weight: 1 })
+const numberValue = fc.oneof(
+  { arbitrary: fc.integer({ max: 10, min: -1 }), weight: 6 },
+  { arbitrary: fc.double({ noDefaultInfinity: true, noNaN: true }), weight: 2 },
+  { arbitrary: fc.constant(-0), weight: 1 },
+)
 
 // V8's JSON.parse returns a wrong key after parsing a key holding an escaped backslash (https://issues.chromium.org/issues/521080746); Bun is unaffected.
 const keyPiece = fc
@@ -73,18 +78,35 @@ function heldAttributes(held: Readonly<Record<string, JsonValue | undefined>>):
   return attrs
 }
 
+// An empty attrs, content or marks key, and adjacent text CommonMark would read back as one, stay occasional: each takes a spelling outside CommonMark.
+// The copy gives fast-check's null-prototype records the prototype a parsed node has.
+function occasionallyEmpty<T extends AdfMark | AdfNode>(arbitrary: Arbitrary<T>): Arbitrary<T> {
+  return fc.tuple(arbitrary, fc.nat({ max: 9 })).map(([held, roll]) => (roll === 0 ? { ...held } : withoutEmptyKeys(held)))
+}
+
+function withoutEmptyKeys<T extends AdfMark | AdfNode>(held: T): T {
+  const kept: Partial<Record<EmptyKey, unknown>> & T = { ...held }
+  for (const key of emptyKeys(held)) delete kept[key]
+  return kept
+}
+
+function occasionallyApart(arbitrary: Arbitrary<AdfNode[]>): Arbitrary<AdfNode[]> {
+  return fc.tuple(arbitrary, fc.nat({ max: 5 })).map(([nodes, roll]) => (roll === 0 ? nodes : mergeAdjacentText(nodes, joinsWhenRead)))
+}
+
 function pipeTable({ body, header }: { body: AdfNode[][]; header: AdfNode[] }): AdfNode {
   const rows = [header, ...body.map((cells) => header.map((_, index) => cells[index] ?? emptyCell))]
   return { content: rows.map((content): AdfNode => ({ content, type: 'tableRow' })), type: 'table' }
 }
 
-const mark: Arbitrary<AdfMark> = fc.oneof(
+const mark: Arbitrary<AdfMark> = occasionallyEmpty(fc.oneof(
   { arbitrary: fc.oneof(...Object.entries(markAttributes).map(([type, vocabulary]) => attributes(vocabulary).map((attrs) => ({ attrs, type })))), weight: 9 },
+  { arbitrary: attributes({ color: 'string' }).map((attrs) => ({ attrs, type: 'backgroundColor' })), weight: 2 },
   { arbitrary: fc.record({ attrs: fc.dictionary(jsonKey, jsonValue, { maxKeys: 2, noNullPrototype: true }), type: unknownType }), weight: 1 },
-)
+))
 const marks = fc.uniqueArray(mark, { maxLength: 3, selector: (held) => held.type })
 
-const textNode = fc.record({ marks, text }).map((held): AdfNode => ({ ...held, type: 'text' }))
+const textNode = occasionallyEmpty(fc.record({ marks, text: fc.oneof({ arbitrary: text, weight: 19 }, { arbitrary: fc.constant(''), weight: 1 }) }).map((held): AdfNode => ({ ...held, type: 'text' })))
 
 const backtickRunNode = fc
   .record({ marks: fc.oneof(fc.constant<AdfMark[]>([]), fc.constant<AdfMark[]>([{ type: 'code' }]), marks), text: fc.string({ maxLength: 6, minLength: 1, unit: fc.constantFrom('`', '``', ' ', 'a') }) })
@@ -95,7 +117,7 @@ const autolinkTextNode = fc
   .map(({ href, marks: held }): AdfNode => ({ marks: [...held.filter((outer) => outer.type !== 'link'), { attrs: { href }, type: 'link' }], text: href, type: 'text' }))
 
 const inlineArbitraries = Object.entries(inlineNodes).map(([type, model]) =>
-  fc.record({ attrs: attributes(model.attributes), marks }).map((held): AdfNode => ({ ...held, type })),
+  occasionallyEmpty(fc.record({ attrs: attributes(model.attributes), marks }).map((held): AdfNode => ({ ...held, type }))),
 )
 
 function weighted(arbitraries: readonly Arbitrary<AdfNode>[], weight: number): { arbitrary: Arbitrary<AdfNode>; weight: number }[] {
@@ -104,10 +126,10 @@ function weighted(arbitraries: readonly Arbitrary<AdfNode>[], weight: number): {
 
 const positions = fc.letrec<Positions>((tie) => {
   const blockContent = fc.array(tie('block'), { depthIdentifier, maxLength: 3 })
-  const inlineContent = fc.array(tie('inline'), { depthIdentifier, maxLength: 4 })
+  const inlineContent = occasionallyApart(fc.array(tie('inline'), { depthIdentifier, maxLength: 4 }))
   const contentByModel = {
     block: blockContent,
-    code: fc.array(text.map((held): AdfNode => ({ text: held, type: 'text' })), { maxLength: 2 }),
+    code: occasionallyApart(fc.array(text.map((held): AdfNode => ({ text: held, type: 'text' })), { maxLength: 2 })),
     inline: inlineContent,
     none: fc.constant<AdfNode[]>([]),
   }
@@ -115,31 +137,40 @@ const positions = fc.letrec<Positions>((tie) => {
   const blockArbitraries = Object.entries(blockNodes).map(([type, model]) => {
     const argument = blockArgument(type)
     const vocabulary: AttributeVocabulary = argument === undefined ? model.attributes : { ...model.attributes, [argument]: 'string' }
-    const node = fc.record({ attrs: attributes(vocabulary), content: contentByModel[model.contentModel], marks: blockMarks }).map((held): AdfNode => ({ ...held, type }))
+    const node = occasionallyEmpty(fc.record({ attrs: attributes(vocabulary), content: contentByModel[model.contentModel], marks: blockMarks }).map((held): AdfNode => ({ ...held, type })))
     return { leaf: model.contentModel === 'code' || model.contentModel === 'none', node }
   })
-  const unknownNode = fc
+  const unknownNode = occasionallyEmpty(
-    .record({ attrs: fc.dictionary(jsonKey, jsonValue, { maxKeys: 2, noNullPrototype: true }), content: fc.array(tie('inline'), { depthIdentifier, maxLength: 2 }), marks, type: unknownType })
+    fc.record({ attrs: fc.dictionary(jsonKey, jsonValue, { maxKeys: 2, noNullPrototype: true }), content: fc.array(tie('inline'), { depthIdentifier, maxLength: 2 }), marks, type: unknownType }),
-    .map((held): AdfNode => held)
+  )
   const leafBlocks = blockArbitraries.filter((entry) => entry.leaf).map((entry) => entry.node)
   const containerBlocks = blockArbitraries.filter((entry) => !entry.leaf).map((entry) => entry.node)
   const misplacedWeight = 7
-  const paragraph = fc.oneof({ arbitrary: inlineContent, weight: 3 }, { arbitrary: fc.array(backtickRunNode, { maxLength: 4, minLength: 2 }), weight: 1 }).map((content): AdfNode => ({ content, type: 'paragraph' }))
+  const paragraph = occasionallyEmpty(
+    fc.oneof({ arbitrary: inlineContent, weight: 3 }, { arbitrary: occasionallyApart(fc.array(backtickRunNode, { maxLength: 4, minLength: 2 })), weight: 1 }).map((content): AdfNode => ({ content, type: 'paragraph' })),
+  )
   const cell = (type: string) => paragraph.map((held): AdfNode => ({ content: [held], type }))
   const listItems = fc.array(
-    blockContent.map((content): AdfNode => ({ content, type: 'listItem' })),
+    occasionallyEmpty(blockContent.map((content): AdfNode => ({ content, type: 'listItem' }))),
     { depthIdentifier, maxLength: 3, minLength: 1 },
   )
   const flatCommonMarkShapes = [
-    fc.record({ content: inlineContent, level: fc.integer({ max: 6, min: 1 }) }).map(({ content, level }): AdfNode => ({ attrs: { level }, content, type: 'heading' })),
+    occasionallyEmpty(fc.record({ content: inlineContent, level: fc.integer({ max: 6, min: 1 }) }).map(({ content, level }): AdfNode => ({ attrs: { level }, content, type: 'heading' }))),
     paragraph,
     fc.record({ body: fc.array(fc.array(cell('tableCell'), { maxLength: 3 }), { maxLength: 2 }), header: fc.array(cell('tableHeader'), { maxLength: 3, minLength: 1 }) }).map(pipeTable),
   ]
+  const task = (type: string, content: Arbitrary<AdfNode[]>) =>
+    occasionallyEmpty(fc.record({ content, state: fc.constantFrom('DONE', 'TODO') }).map(({ content: held, state }): AdfNode => ({ attrs: { state }, content: held, type })))
+  const taskItem = fc.oneof({ arbitrary: task('taskItem', inlineContent), weight: 3 }, { arbitrary: task('blockTaskItem', blockContent), weight: 1 })
   const nestingCommonMarkShapes = [
-    blockContent.map((content): AdfNode => ({ content, type: 'blockquote' })),
+    occasionallyEmpty(blockContent.map((content): AdfNode => ({ content, type: 'blockquote' }))),
+    fc.array(fc.oneof({ arbitrary: taskItem, weight: 3 }, { arbitrary: tie('block'), weight: 1 }), { depthIdentifier, maxLength: 3, minLength: 1 }).map((content): AdfNode => ({ content, type: 'taskList' })),
     listItems.map((content): AdfNode => ({ content, type: 'bulletList' })),
     fc
-      .record({ content: listItems, order: fc.oneof({ arbitrary: fc.integer({ max: 3, min: 0 }), weight: 4 }, { arbitrary: fc.integer({ max: 999999999, min: 0 }), weight: 1 }) })
+      .record({
+        content: listItems,
+        order: fc.oneof({ arbitrary: fc.integer({ max: 3, min: 0 }), weight: 8 }, { arbitrary: fc.integer({ max: 999999999, min: 0 }), weight: 2 }, { arbitrary: fc.constant(-0), weight: 1 }),
+      })
       .map(({ content, order }): AdfNode => ({ attrs: { order }, content, type: 'orderedList' })),
   ]
   const flatBlocks = [...weighted(leafBlocks, 2), ...weighted(flatCommonMarkShapes, flatCommonMarkShapeWeight)]
@@ -162,7 +193,11 @@ const positions = fc.letrec<Positions>((tie) => {
   }
 })
 
-export const adfDocument = fc.array(positions.block, { depthIdentifier, maxLength: 4, minLength: 1 }).map((content): AdfDocument => toEditorNormal({ content, type: 'doc', version: 1 }))
+export const adfDocument = fc.oneof(
+  { arbitrary: fc.array(positions.block, { depthIdentifier, maxLength: 4, minLength: 1 }).map((content): AdfDocument => ({ content, type: 'doc', version: 1 })), weight: 30 },
+  { arbitrary: fc.constant<AdfDocument>({ content: [], type: 'doc', version: 1 }), weight: 1 },
+  { arbitrary: fc.constant<AdfDocument>({ type: 'doc', version: 1 }), weight: 1 },
+)
 
 export function propertyRuns(gateRuns: number): { gate: boolean; numRuns: number; seed?: number } {
   const deepRuns = env[deepRunsVariable]

src/index.ts

@@ -1,7 +1,8 @@
+// Export only the conversions, their types, isAdfDocument and what a guarantee or a persona needs.
 export type { AdfAttributes, AdfDocument, AdfMark, AdfNode } from './adf/document.ts'
 export type { ConvertError, ConvertErrorCode, ConvertErrorPath, ParseError, Result, SourcePosition } from './result.ts'
 export type { JsonValue } from './json-value.ts'
 export { adfToMarkdown } from './markdown/emit/adf-to-markdown.ts'
-export { adfToPlainMarkdown } from './markdown/emit/plain-reduction.ts'
+export { adfToPlainMarkdown } from './markdown/plain/adf-to-plain-markdown.ts'
 export { isAdfDocument } from './adf/document.ts'
 export { markdownToAdf, plainMarkdownToAdf } from './markdown/parse/markdown-to-adf.ts'

src/markdown/adjacent-text.ts

@@ -0,0 +1,12 @@
+import type { AdfNode } from '../adf/document.ts'
+import { identicalMarks, isBareText, nodeMarks } from '../adf/document.ts'
+import { spellInlineLeafDirective } from './directive-syntax.ts'
+
+export const textBreakName = 'textBreak'
+
+export const textBreakSpelling = spellInlineLeafDirective(textBreakName, '')
+
+// The lossless reader's rule: CommonMark reads the pair back as one text run (spec/flavour.md, Inline nodes).
+export function joinsWhenRead(previous: AdfNode, node: AdfNode): boolean {
+  return isBareText(previous) && isBareText(node) && identicalMarks(nodeMarks(previous), nodeMarks(node))
+}

src/markdown/block-directive.ts

@@ -2,9 +2,9 @@ import type { AdfMark } from '../adf/document.ts'
 import type { BlockType } from '../adf/block-nodes.ts'
 import type { JsonValue } from '../json-value.ts'
 import { blockNodeModel } from '../adf/block-nodes.ts'
-import { isAdfMark, nodeAttrs } from '../adf/document.ts'
+import { isAdfMark } from '../adf/document.ts'
 import { serializeCanonicalJson } from '../canonical-json.ts'
-import { spellDirectiveOpener } from './directive-syntax.ts'
+import { spellAttributes, spellDirectiveOpener } from './directive-syntax.ts'
 
 const argumentByType = new Map(
   Object.entries({
@@ -14,6 +14,13 @@ const argumentByType = new Map(
   } satisfies Partial<Record<BlockType, string>>),
 )
 
+export const documentName = 'doc'
+
+// spec/flavour.md, Directives: a document holding no content key, which the empty string cannot spell.
+export const documentAttribute = { key: 'content', value: 'none' }
+
+export const documentSpelling = spellDirectiveOpener(documentName, undefined, spellAttributes([[documentAttribute.key, documentAttribute.value]]))
+
 export const listBreakName = 'listBreak'
 
 export const listBreakSpelling = spellDirectiveOpener(listBreakName, undefined, '')
@@ -25,17 +32,14 @@ export function blockArgument(type: string): string | undefined {
 }
 
 export function blockDirectiveForm(name: string): 'container' | 'leaf' | undefined {
-  if (name === listBreakName) return 'leaf'
+  if (name === listBreakName || name === documentName) return 'leaf'
   const model = blockNodeModel(name)
   if (model === undefined) return undefined
   return model.contentModel === 'none' ? 'leaf' : 'container'
 }
 
 export function markValues(marks: readonly AdfMark[]): JsonValue {
-  return marks.map((mark) => {
+  return marks.map((mark) => (mark.attrs === undefined ? { type: mark.type } : { attrs: mark.attrs, type: mark.type }))
-    const attrs = nodeAttrs(mark)
-    return Object.keys(attrs).length === 0 ? { type: mark.type } : { attrs, type: mark.type }
-  })
 }
 
 export function readMarkValues(value: JsonValue): AdfMark[] | undefined {

src/markdown/code-language.ts

@@ -1,14 +1,12 @@
 import type { JsonValue } from '../json-value.ts'
-import { carryName } from './opaque-carry.ts'
+import { carryFenceType } from './opaque-carry.ts'
-import { holdsControlCharacter } from './commonmark/grammar.ts'
+import { infoStringCarries } from './commonmark/grammar.ts'
-import { holdsEntityReference } from './commonmark/entity-references.ts'
 
 export type LanguageSlot = { info: string; kind: 'fence' } | { kind: 'attribute' } | { kind: 'none' }
 
 // spec/flavour.md, The CommonMark blocks: the one slot a codeBlock's language rides.
 export function languageSlot(language: JsonValue | undefined): LanguageSlot {
   if (language === undefined) return { kind: 'none' }
-  if (typeof language !== 'string' || language === '' || language === carryName) return { kind: 'attribute' }
+  if (typeof language !== 'string' || carryFenceType(language) !== undefined || !infoStringCarries(language)) return { kind: 'attribute' }
-  if (/[`\\]/.test(language) || holdsControlCharacter(language) || language !== language.trim() || holdsEntityReference(language)) return { kind: 'attribute' }
   return { info: language, kind: 'fence' }
 }

src/markdown/commonmark/grammar.ts

@@ -1,4 +1,4 @@
-import { readEntityReference, replacementCharacter } from './entity-references.ts'
+import { holdsEntityReference, readEntityReference, replacementCharacter } from './entity-references.ts'
 
 export type LinePosition = 'first' | 'later'
 
@@ -83,10 +83,6 @@ export function backslashEscape(text: string, index: number): string | undefined
   return isAsciiPunctuation(escaped) ? escaped : undefined
 }
 
-export function claimsLine(line: string, position: LinePosition): boolean {
-  return escapesLineClaim(line, 0, position) || orderedListOpener.test(line)
-}
-
 export function claimsPipeLine(line: string): boolean {
   return pipeClaim.test(line)
 }
@@ -133,6 +129,11 @@ export function holdsControlCharacter(text: string): boolean {
   return controlCharacter.test(text)
 }
 
+// What a backtick fence's info string reads back verbatim: escapes and entity references decode, and the edges trim.
+export function infoStringCarries(text: string): boolean {
+  return text !== '' && !/[`\\]/.test(text) && !holdsControlCharacter(text) && text === text.trim() && !holdsEntityReference(text)
+}
+
 export function holdsNullCharacter(text: string): boolean {
   return nullCharacter.test(text)
 }

src/markdown/commonmark/link-syntax.ts

@@ -1,4 +1,4 @@
-import { backslashEscape, decodeTextEscapes, holdsControlCharacter } from './grammar.ts'
+import { backslashEscape, decodeTextEscapes, holdsControlCharacter, holdsNullCharacter } from './grammar.ts'
 import { holdsEntityReference } from './entity-references.ts'
 
 export type LinkDefinition = { destination: string; title?: string }
@@ -117,5 +117,5 @@ export function escapeUnbalanced(spelling: string, opener: string, closer: strin
 }
 
 function spellTitle(title: string): string | undefined {
-  return /[\n\r\\]/.test(title) || holdsEntityReference(title) ? undefined : ` "${title.replaceAll('"', '\\"')}"`
+  return /[\n\r\\]/.test(title) || holdsNullCharacter(title) || holdsEntityReference(title) ? undefined : ` "${title.replaceAll('"', '\\"')}"`
 }

src/markdown/directive-syntax.ts

@@ -1,7 +1,7 @@
 import type { AttributeKind, VocabularyPair, VocabularyValue } from '../adf/attribute-vocabulary.ts'
 import type { ConvertFault } from '../result.ts'
 import type { JsonValue } from '../json-value.ts'
-import { backslashEscape } from './commonmark/grammar.ts'
+import { backslashEscape, holdsNullCharacter } from './commonmark/grammar.ts'
 import { backtickRun, closingBacktickRun } from './commonmark/backtick-runs.ts'
 import { isJsonValue, overNested } from '../json-value.ts'
 import { largestNesting } from '../nesting.ts'
@@ -100,10 +100,10 @@ export function readSoleStringAttribute(span: DirectiveSpan, key: string): Read<
   return { value: spelled.decoded }
 }
 
-// Both directions answer alike: an inline directive never spans lines, so no content slot holds a line ending.
+// An inline directive never spans lines, and no content slot holds a null character; the emitter carries such a node.
-export function slotLineEndingFault(type: string, text: string): ConvertFault | undefined {
+export function slotFault(type: string, text: string): ConvertFault | undefined {
-  if (!/[\n\r]/.test(text)) return undefined
+  if (/[\n\r]/.test(text)) return { code: 'unspellable-whitespace', message: `the ${type} content slot holds a newline no inline directive spans` }
-  return { code: 'unspellable-whitespace', message: `the ${type} content slot holds a newline no inline directive spans` }
+  return holdsNullCharacter(text) ? unsupportedNodeShape(`the ${type} content slot holds a null character: write the node as !adf:carry`) : undefined
 }
 
 export function spellAttributes(pairs: readonly (readonly [string, string])[]): string {
@@ -139,7 +139,7 @@ export function spellStringAttribute(text: string): string {
 export function spellAttributeValue(value: VocabularyValue): string {
   if (value.kind === 'boolean') return `${value.value}`
   if (value.kind === 'json') return spellJsonAttribute(value.value)
-  if (value.kind === 'number') return spellStringAttribute(JSON.stringify(value.value))
+  if (value.kind === 'number') return spellStringAttribute(serializeCanonicalJson(value.value, 'compact'))
   return spellStringAttribute(value.value)
 }
 

src/markdown/emit/adf-to-markdown.test.ts

@@ -6,14 +6,13 @@ import type { JsonValue } from '../../json-value.ts'
 import type { Result } from '../../result.ts'
 import { adfToMarkdown, markdownToAdf } from '../../index.ts'
 import { largestNesting } from '../../nesting.ts'
-import { toEditorNormal } from '../../adf/editor-normal.ts'
 
 function document(...content: AdfNode[]): AdfDocument {
   return { content, type: 'doc', version: 1 }
 }
 
 function paragraph(...content: AdfNode[]): AdfNode {
-  return { content, type: 'paragraph' }
+  return content.length === 0 ? { type: 'paragraph' } : { content, type: 'paragraph' }
 }
 
 function code(result: Result<string>): string {
@@ -36,7 +35,7 @@ test('names the node a refusal came from, and no source the emitter never read',
   const unspellable: AdfNode = { text: 'x', type: 'paragraph' }
   const list: AdfNode = { content: [{ content: [paragraph({ text: 'x', type: 'text' })], type: 'listItem' }, { content: [unspellable], type: 'listItem' }], type: 'bulletList' }
   assert.deepEqual(path(adfToMarkdown(document(paragraph({ text: 'x', type: 'text' }), list))), ['content', 1, 'content', 1, 'content', 0])
-  assert.deepEqual(path(adfToMarkdown(document(paragraph({ text: 'x', type: 'text' }, { type: 'text' })))), ['content', 0, 'content', 1])
+  assert.deepEqual(path(adfToMarkdown(document(paragraph({ text: 'x', type: 'text' }, { text: 'x', type: 'status' })))), ['content', 0, 'content', 1])
   assert.deepEqual(path(adfToMarkdown({ type: 'doc', version: 2 })), [])
   assert.equal(position(adfToMarkdown(document(paragraph({ text: 'x', type: 'text' }), list))), undefined)
 })
@@ -148,8 +147,16 @@ test('carries a mark the canonical spellings cannot nest', () => {
   )
 })
 
-test('refuses a line whose start block parsing would claim', () => {
+function readsBack(doc: AdfDocument): string {
-  assert.equal(code(adfToMarkdown(document(paragraph({ marks: [{ type: 'code' }], text: '```', type: 'text' })))), 'unspellable-line-start')
+  const spelled = markdown(adfToMarkdown(doc))
+  assert.deepEqual(markdownToAdf(spelled), { ok: true, value: doc }, `reading ${JSON.stringify(spelled)}`)
+  return spelled
+}
+
+test('spells a code span opening a line, whose backticks open no fence', () => {
+  const fence: AdfNode = { marks: [{ type: 'code' }], text: '``', type: 'text' }
+  assert.equal(readsBack(document(paragraph(fence))), '``` `` ```\n')
+  assert.equal(readsBack(document(paragraph({ text: 'a', type: 'text' }, { type: 'hardBreak' }, fence))), 'a\\\n``` `` ```\n')
 })
 
 test('escapes the delimiter row a hard break leaves opening a pipe table with no leading pipe', () => {
@@ -168,21 +175,24 @@ test('parts two adjacent lists of the same kind, the marker spelling being what
   const nested: AdfNode = { content: [{ content: [list, list], type: 'listItem' }], type: 'bulletList' }
   assert.equal(markdown(adfToMarkdown(document(nested))), '- - x\n\n  !adf:listBreak\n\n  - x\n')
   const carried: AdfNode = { ...list, attrs: { unknown: 'x' } }
-  assert.ok(markdown(adfToMarkdown(document(carried, carried))).includes('```\n\n```carry\n'))
+  assert.ok(markdown(adfToMarkdown(document(carried, carried))).includes('```\n\n```adf:bulletList\n'))
   assert.ok(markdown(adfToMarkdown(document(carried, list))).endsWith('```\n\n- x\n'))
-  assert.ok(markdown(adfToMarkdown(document(list, carried))).startsWith('- x\n\n```carry\n'))
+  assert.ok(markdown(adfToMarkdown(document(list, carried))).startsWith('- x\n\n```adf:bulletList\n'))
 })
 
-test('carries a node type no section spells', () => {
+test('carries a node type no section spells, the fence naming the type wherever an info string carries it', () => {
-  assert.equal(markdown(adfToMarkdown(document({ type: 'blockCard' }))), '```carry\n{\n  "type": "blockCard"\n}\n```\n')
+  assert.equal(markdown(adfToMarkdown(document({ type: 'blockCard' }))), '```adf:blockCard\n{}\n```\n')
-  assert.equal(markdown(adfToMarkdown(document({ type: 'toString' }))), '```carry\n{\n  "type": "toString"\n}\n```\n')
+  assert.equal(markdown(adfToMarkdown(document({ type: 'toString' }))), '```adf:toString\n{}\n```\n')
   assert.equal(markdown(adfToMarkdown(document(paragraph({ type: 'blockCard' })))), '!adf:carry{json="{\\"type\\":\\"blockCard\\"}"}\n')
-  assert.equal(markdown(adfToMarkdown(document({ text: 'x', type: 'text' }))), '```carry\n{\n  "text": "x",\n  "type": "text"\n}\n```\n')
+  assert.equal(markdown(adfToMarkdown(document({ text: 'x', type: 'text' }))), '```adf:text\n{\n  "text": "x"\n}\n```\n')
-  assert.equal(markdown(adfToMarkdown(document({ type: 'hardBreak' }))), '```carry\n{\n  "type": "hardBreak"\n}\n```\n')
+  assert.equal(markdown(adfToMarkdown(document({ type: 'hardBreak' }))), '```adf:hardBreak\n{}\n```\n')
+  assert.equal(markdown(adfToMarkdown(document({ type: 'a&amp;b' }))), '```adf:\n{\n  "type": "a&amp;b"\n}\n```\n')
+  assert.equal(markdown(adfToMarkdown(document({ type: 'a\\b' }))), '```adf:\n{\n  "type": "a\\\\b"\n}\n```\n')
 })
 
-test('spells the code block whose language is the reserved info string', () => {
+test('spells the code block whose language opens with the reserved info string prefix', () => {
-  assert.equal(markdown(adfToMarkdown(document({ attrs: { language: 'carry' }, type: 'codeBlock' }))), '!adf:codeBlock {language=carry}\n```\n```\n!adf:/codeBlock\n')
+  assert.equal(markdown(adfToMarkdown(document({ attrs: { language: 'adf:x' }, type: 'codeBlock' }))), '!adf:codeBlock {language="adf:x"}\n```\n```\n!adf:/codeBlock\n')
+  assert.equal(markdown(adfToMarkdown(document({ attrs: { language: 'carry' }, type: 'codeBlock' }))), '```carry\n```\n')
   assert.equal(markdown(adfToMarkdown(document({ attrs: { language: 'adf' }, type: 'codeBlock' }))), '```adf\n```\n')
 })
 
@@ -208,21 +218,17 @@ test('refuses a carried node nested deeper than the levels its position leaves',
   assert.equal(code(adfToMarkdown(document(quoted))), 'unsupported-nesting-depth')
 })
 
-test('refuses a node whose content model the canonical form cannot emit', () => {
+test('carries a code block holding a node no fence holds', () => {
-  assert.equal(
+  assert.equal(markdown(adfToMarkdown(document({ content: [paragraph()], type: 'codeBlock' }))), '```adf:codeBlock\n{\n  "content": [\n    {\n      "type": "paragraph"\n    }\n  ]\n}\n```\n')
-    markdown(adfToMarkdown(document({ content: [paragraph()], type: 'codeBlock' }))),
+  for (const child of [{ attrs: {}, text: 'x', type: 'text' }, { content: [], text: 'x', type: 'text' }, { marks: [], text: 'x', type: 'text' }, { content: [{ text: 'lost', type: 'text' }], text: 'x', type: 'text' }]) {
-    'unsupported-node-shape: a codeBlock holds plain text nodes only: this paragraph node is not one',
+    assert.ok(markdown(adfToMarkdown(document({ content: [child], type: 'codeBlock' }))).startsWith('```adf:codeBlock\n'), JSON.stringify(child))
-  )
+  }
-  assert.equal(
-    markdown(adfToMarkdown(document({ content: [{ content: [{ text: 'lost', type: 'text' }], text: 'x', type: 'text' }], type: 'codeBlock' }))),
-    'unsupported-node-shape: a codeBlock holds plain text nodes only: this text node is not one',
-  )
 })
 
 test('spells a list its own content shape cannot hold as a directive', () => {
   assert.equal(markdown(adfToMarkdown(document({ content: [paragraph()], type: 'bulletList' }))), '!adf:bulletList\n!adf:paragraph\n!adf:/paragraph\n!adf:/bulletList\n')
   assert.equal(markdown(adfToMarkdown(document({ type: 'bulletList' }))), '!adf:bulletList\n!adf:/bulletList\n')
-  assert.equal(markdown(adfToMarkdown(document({ attrs: { order: 2 }, content: [], type: 'orderedList' }))), '!adf:orderedList {order=2}\n!adf:/orderedList\n')
+  assert.equal(markdown(adfToMarkdown(document({ attrs: { order: 2 }, content: [], type: 'orderedList' }))), '!adf:orderedList {content=empty order=2}\n!adf:/orderedList\n')
 })
 
 test('spells an ordered list no marker fits as a directive', () => {
@@ -334,7 +340,7 @@ test('refuses a node carrying one mark type twice', () => {
 })
 
 test('parts a nested list the tight spelling would swallow from the block above it', () => {
-  const item = (...content: AdfNode[]): AdfNode => ({ content, type: 'listItem' })
+  const item = (...content: AdfNode[]): AdfNode => (content.length === 0 ? { type: 'listItem' } : { content, type: 'listItem' })
   const text = (value: string): AdfNode => ({ content: [{ text: value, type: 'text' }], type: 'paragraph' })
   const outer = (...content: AdfNode[]): AdfDocument => document({ content: [item(...content)], type: 'bulletList' })
   const ordered: AdfNode = { attrs: { order: 2 }, content: [item(text('b'))], type: 'orderedList' }
@@ -345,7 +351,7 @@ test('parts a nested list the tight spelling would swallow from the block above
   const list: AdfNode = { content: [item(text('b'))], type: 'bulletList' }
   const panel: AdfNode = { attrs: { panelType: 'info' }, content: [text('p')], type: 'panel' }
   assert.equal(markdown(adfToMarkdown(outer(panel, list))), '- !adf:panel info\n  p\n  !adf:/panel\n\n  - b\n')
-  assert.ok(markdown(adfToMarkdown(outer(text('a'), { ...list, attrs: { unknown: 'x' } }))).startsWith('- a\n\n  ```carry\n'))
+  assert.ok(markdown(adfToMarkdown(outer(text('a'), { ...list, attrs: { unknown: 'x' } }))).startsWith('- a\n\n  ```adf:bulletList\n'))
 })
 
 test('refuses marks and attributes nested deeper than the emitter carries', () => {
@@ -372,7 +378,7 @@ test('refuses marks and attributes nested deeper than the emitter carries', () =
     assert.ok(spelled.ok, spelled.ok ? '' : spelled.error.message)
     const read = markdownToAdf(spelled.value)
     assert.ok(read.ok, read.ok ? '' : read.error.message)
-    assert.deepEqual(toEditorNormal(read.value), document(node))
+    assert.deepEqual(read.value, document(node))
   }
 
   assert.equal(markdown(adfToMarkdown(document(paragraph({ marks: [{ attrs, type: 'em' }], text: 'x', type: 'text' })))), deeper('depth', 'em'))
@@ -442,7 +448,7 @@ test('escapes a hyphen underline a hard break would expose', () => {
 })
 
 test('spells a list item whose marker completes a thematic break as a directive', () => {
-  const item = (...content: AdfNode[]): AdfNode => ({ content, type: 'listItem' })
+  const item = (...content: AdfNode[]): AdfNode => (content.length === 0 ? { type: 'listItem' } : { content, type: 'listItem' })
   assert.equal(markdown(adfToMarkdown(document({ content: [item({ type: 'rule' })], type: 'bulletList' }))), '!adf:bulletList\n!adf:listItem\n---\n!adf:/listItem\n!adf:/bulletList\n')
   const nested: AdfNode = { content: [item({ content: [item()], type: 'bulletList' })], type: 'bulletList' }
   assert.equal(markdown(adfToMarkdown(document(nested))), '- -\n')
@@ -458,31 +464,26 @@ test('spells a list item whose marker completes a thematic break as a directive'
   )
 })
 
-test('refuses the characters CommonMark rewrites', () => {
+test('spells the characters CommonMark rewrites', () => {
-  assert.equal(
+  assert.equal(readsBack(document(paragraph({ text: 'a\r\r\nb', type: 'text' }))), 'a&#13;&#13;!adf:text{text="\\n"}b\n')
-    markdown(adfToMarkdown(document({ content: [{ text: 'a\rb', type: 'text' }], type: 'codeBlock' }))),
+  assert.equal(readsBack(document(paragraph({ marks: [{ type: 'strong' }], text: '\u0000\u0000a\u0000', type: 'text' }))), '**!adf:text{text="\\u0000\\u0000"}a!adf:text{text="\\u0000"}**\n')
-    'unspellable-character: a codeBlock holds no carriage return CommonMark keeps: this text holds one',
+  assert.equal(readsBack(document(paragraph({ marks: [{ attrs: { href: 'u' }, type: 'link' }], text: 'a\rb\u0000', type: 'text' }))), '[a&#13;b!adf:text{text="\\u0000"}](u)\n')
-  )
+  assert.equal(readsBack(document({ attrs: { level: 1 }, content: [{ text: '\r', type: 'text' }], type: 'heading' })), '# &#13;\n')
-  assert.equal(
+  assert.equal(readsBack(document({ content: [{ text: 'a\rb', type: 'text' }], type: 'codeBlock' })), '```adf:codeBlock\n{\n  "content": [\n    {\n      "text": "a\\rb",\n      "type": "text"\n    }\n  ]\n}\n```\n')
-    markdown(adfToMarkdown(document(paragraph({ text: 'a\rb', type: 'text' })))),
+  readsBack(document({ content: [{ text: 'a\u0000b', type: 'text' }], type: 'codeBlock' }))
-    'unspellable-character: a text node holds a carriage return CommonMark rewrites',
+  readsBack(document(paragraph({ marks: [{ type: 'code' }], text: 'a\u0000b', type: 'text' })))
-  )
-  assert.equal(code(adfToMarkdown(document(paragraph({ text: 'a\u0000b', type: 'text' })))), 'unspellable-character')
-  assert.equal(code(adfToMarkdown(document({ content: [{ text: 'a\u0000b', type: 'text' }], type: 'codeBlock' }))), 'unspellable-character')
-  assert.equal(
-    markdown(adfToMarkdown(document({ content: [{ text: '', type: 'text' }], type: 'codeBlock' }))),
-    'unsupported-node-shape: a codeBlock holds plain text nodes only: this text node is not one',
-  )
 })
 
-test('refuses a text node the spelling would empty out', () => {
+test('carries a text node holding no text, or holding content', () => {
   const nested: AdfNode[] = [{ text: 'lost', type: 'text' }]
-  const empty = 'unsupported-node-shape: a text node holds text: this one has none'
+  assert.equal(readsBack(document(paragraph({ text: '', type: 'text' }))), '!adf:carry{json="{\\"text\\":\\"\\",\\"type\\":\\"text\\"}"}\n')
-  const holding = 'unsupported-node-shape: a text node holds no content: this one holds some'
+  assert.equal(readsBack(document(paragraph({ type: 'text' }, { text: 'a', type: 'text' }))), '!adf:carry{json="{\\"type\\":\\"text\\"}"}a\n')
-  assert.equal(markdown(adfToMarkdown(document(paragraph({ text: '', type: 'text' })))), empty)
+  readsBack(document(paragraph({ marks: [{ type: 'code' }], text: '', type: 'text' })))
-  assert.equal(markdown(adfToMarkdown(document(paragraph({ marks: [{ type: 'code' }], text: '', type: 'text' })))), empty)
+  readsBack(document(paragraph({ marks: [{ type: 'em' }], text: 'a', type: 'text' }, { marks: [{ type: 'em' }], text: '', type: 'text' })))
-  assert.equal(markdown(adfToMarkdown(document(paragraph({ content: nested, text: 'x', type: 'text' })))), holding)
+  readsBack(document(paragraph({ content: nested, text: 'x', type: 'text' })))
-  assert.equal(markdown(adfToMarkdown(document(paragraph({ content: nested, marks: [{ type: 'code' }], text: 'x', type: 'text' })))), holding)
+  readsBack(document(paragraph({ content: nested, marks: [{ type: 'code' }], text: 'x', type: 'text' })))
+  readsBack(document({ content: [{ text: '', type: 'text' }], type: 'codeBlock' }))
+  readsBack(document({ content: [{ text: 'a', type: 'text' }, { type: 'text' }], type: 'codeBlock' }))
 })
 
 test('carries a mark run whose edge holds whitespace CommonMark flanking counts', () => {
@@ -501,11 +502,11 @@ test('pads a code span whose edges CommonMark would strip', () => {
   assert.equal(markdown(adfToMarkdown(document(paragraph({ marks: [{ type: 'code' }], text: ' \t ', type: 'text' })))), '`  \t  `\n')
 })
 
-test('spells one code span over a run of code-marked nodes', () => {
+test('spells a code span per code-marked node, parted by the text break', () => {
   const code_ = { type: 'code' }
   assert.equal(
     markdown(adfToMarkdown(document(paragraph({ marks: [code_], text: 'a', type: 'text' }, { marks: [code_], text: 'b', type: 'text' })))),
-    '`ab`\n',
+    '`a`!adf:textBreak{}`b`\n',
   )
 })
 
@@ -545,7 +546,7 @@ test('emits an empty list item without trailing whitespace', () => {
 test('spells a block directive as its node type, arg and attributes', () => {
   const panel = (attrs: AdfAttributes): AdfDocument => document({ attrs, content: [paragraph({ text: 'x', type: 'text' })], type: 'panel' })
   assert.equal(markdown(adfToMarkdown(panel({ panelType: 'warning' }))), '!adf:panel warning\nx\n!adf:/panel\n')
-  assert.equal(markdown(adfToMarkdown(panel({}))), '!adf:panel\nx\n!adf:/panel\n')
+  assert.equal(markdown(adfToMarkdown(panel({}))), '!adf:panel {attrs=empty}\nx\n!adf:/panel\n')
   assert.equal(markdown(adfToMarkdown(document({ content: [{ text: 'x', type: 'text' }], type: 'caption' }))), '!adf:caption\nx\n!adf:/caption\n')
   assert.equal(markdown(adfToMarkdown(document({ type: 'caption' }))), '!adf:caption\n!adf:/caption\n')
   assert.equal(markdown(adfToMarkdown(document({ attrs: { localId: 'a' }, type: 'syncBlock' }))), '!adf:syncBlock {localId=a}\n')
@@ -553,20 +554,20 @@ test('spells a block directive as its node type, arg and attributes', () => {
 
 test('carries a directive attribute no section spells', () => {
   const carried = (node: AdfNode): string => markdown(adfToMarkdown(document(node)))
-  assert.equal(carried({ attrs: { rounded: true }, type: 'panel' }), '```carry\n{\n  "attrs": {\n    "rounded": true\n  },\n  "type": "panel"\n}\n```\n')
+  assert.equal(carried({ attrs: { rounded: true }, type: 'panel' }), '```adf:panel\n{\n  "attrs": {\n    "rounded": true\n  }\n}\n```\n')
-  assert.equal(carried({ attrs: { toString: 'x' }, type: 'panel' }), '```carry\n{\n  "attrs": {\n    "toString": "x"\n  },\n  "type": "panel"\n}\n```\n')
+  assert.equal(carried({ attrs: { toString: 'x' }, type: 'panel' }), '```adf:panel\n{\n  "attrs": {\n    "toString": "x"\n  }\n}\n```\n')
-  assert.equal(carried({ attrs: { localId: 4 }, type: 'panel' }), '```carry\n{\n  "attrs": {\n    "localId": 4\n  },\n  "type": "panel"\n}\n```\n')
+  assert.equal(carried({ attrs: { localId: 4 }, type: 'panel' }), '```adf:panel\n{\n  "attrs": {\n    "localId": 4\n  }\n}\n```\n')
   assert.equal(
     carried({ attrs: { width: '50' }, type: 'layoutColumn' }),
-    '```carry\n{\n  "attrs": {\n    "width": "50"\n  },\n  "type": "layoutColumn"\n}\n```\n',
+    '```adf:layoutColumn\n{\n  "attrs": {\n    "width": "50"\n  }\n}\n```\n',
   )
   assert.equal(
     carried({ attrs: { isNumberColumnEnabled: 'true' }, type: 'table' }),
-    '```carry\n{\n  "attrs": {\n    "isNumberColumnEnabled": "true"\n  },\n  "type": "table"\n}\n```\n',
+    '```adf:table\n{\n  "attrs": {\n    "isNumberColumnEnabled": "true"\n  }\n}\n```\n',
   )
   assert.equal(
     carried({ content: [{ attrs: { alt: 4 }, type: 'media' }], type: 'mediaGroup' }),
-    '!adf:mediaGroup\n```carry\n{\n  "attrs": {\n    "alt": 4\n  },\n  "type": "media"\n}\n```\n!adf:/mediaGroup\n',
+    '!adf:mediaGroup\n```adf:media\n{\n  "attrs": {\n    "alt": 4\n  }\n}\n```\n!adf:/mediaGroup\n',
   )
 })
 
@@ -574,15 +575,16 @@ test('carries an arg slot value no bare token spells', () => {
   const carried = (node: AdfNode): string => markdown(adfToMarkdown(document(node)))
   assert.equal(
     carried({ attrs: { panelType: 'extra info' }, type: 'panel' }),
-    '```carry\n{\n  "attrs": {\n    "panelType": "extra info"\n  },\n  "type": "panel"\n}\n```\n',
+    '```adf:panel\n{\n  "attrs": {\n    "panelType": "extra info"\n  }\n}\n```\n',
   )
-  assert.equal(carried({ attrs: { state: 2 }, type: 'taskItem' }), '```carry\n{\n  "attrs": {\n    "state": 2\n  },\n  "type": "taskItem"\n}\n```\n')
+  assert.equal(carried({ attrs: { state: 2 }, type: 'taskItem' }), '```adf:taskItem\n{\n  "attrs": {\n    "state": 2\n  }\n}\n```\n')
 })
 
 test('carries a block node mark in the reserved attribute', () => {
   const section = (...marks: AdfMark[]): AdfDocument => document({ marks, type: 'layoutSection' })
   assert.equal(markdown(adfToMarkdown(section({ type: 'breakout' }))), '!adf:layoutSection {marks="[{\\"type\\":\\"breakout\\"}]"}\n!adf:/layoutSection\n')
-  assert.equal(markdown(adfToMarkdown(section({ attrs: {}, type: 'breakout' }))), '!adf:layoutSection {marks="[{\\"type\\":\\"breakout\\"}]"}\n!adf:/layoutSection\n')
+  assert.equal(markdown(adfToMarkdown(section({ attrs: {}, type: 'breakout' }))), '!adf:layoutSection {marks="[{\\"attrs\\":{},\\"type\\":\\"breakout\\"}]"}\n!adf:/layoutSection\n')
+  assert.equal(markdown(adfToMarkdown(section())), '!adf:layoutSection {marks=empty}\n!adf:/layoutSection\n')
 })
 
 test('refuses the content a directive body has no room for', () => {
@@ -604,7 +606,7 @@ test('separates blocks in a container body by a blank line only where a directiv
 test('spells the image form for exactly the centered external media shape', () => {
   const url = 'https://example.com/moon.png'
   const single = (attrs: AdfAttributes, ...content: AdfNode[]): AdfDocument =>
-    document({ attrs: { layout: 'center' }, content: [{ attrs, content, type: 'media' }], type: 'mediaSingle' })
+    document({ attrs: { layout: 'center' }, content: [content.length === 0 ? { attrs, type: 'media' } : { attrs, content, type: 'media' }], type: 'mediaSingle' })
   assert.equal(markdown(adfToMarkdown(single({ alt: 'The moon', type: 'external', url }))), `![The moon](${url})\n`)
   assert.equal(markdown(adfToMarkdown(single({ type: 'external', url }))), `![](${url})\n`)
   assert.equal(markdown(adfToMarkdown(single({ alt: 'a [b] c', type: 'external', url }))), `![a \\[b\\] c](${url})\n`)
@@ -692,8 +694,12 @@ test('refuses the content and slot an inline directive has no room for', () => {
   assert.equal(refused({ text: 'x', type: 'status' }), neither('status', 'text'))
   assert.equal(refused({ content: [{ text: 'x', type: 'text' }], type: 'hardBreak' }), neither('hardBreak', 'content'))
   assert.equal(refused({ text: 'x', type: 'hardBreak' }), neither('hardBreak', 'text'))
-  assert.equal(refused({ attrs: { text: 'a\nb' }, type: 'status' }), 'unspellable-whitespace: the status content slot holds a newline no inline directive spans')
+})
-  assert.equal(refused({ attrs: { text: 'a\u0000b' }, type: 'status' }), 'unspellable-character: a status content slot holds a null character CommonMark replaces')
+
+test('carries an inline node whose content slot holds a line ending or a null character', () => {
+  assert.equal(readsBack(document(paragraph({ attrs: { text: 'a\nb' }, type: 'status' }))), '!adf:carry{json="{\\"attrs\\":{\\"text\\":\\"a\\\\nb\\"},\\"type\\":\\"status\\"}"}\n')
+  readsBack(document(paragraph({ attrs: { text: 'a\rb' }, type: 'emoji' })))
+  readsBack(document(paragraph({ attrs: { id: 'x', text: 'a\u0000b' }, type: 'mention' })))
 })
 
 test('spells the directive marks around the longest run they cover', () => {
@@ -701,7 +707,8 @@ test('spells the directive marks around the longest run they cover', () => {
   const emitted = (...content: AdfNode[]): string => markdown(adfToMarkdown(document(paragraph(...content))))
   const underline: AdfMark = { type: 'underline' }
   assert.equal(emitted(marked('x', underline)), '!adf:underline[x]\n')
-  assert.equal(emitted(marked('a', underline), marked('b', underline)), '!adf:underline[ab]\n')
+  assert.equal(emitted(marked('a', underline), marked('b', underline)), '!adf:underline[a!adf:textBreak{}b]\n')
+  assert.equal(emitted(marked('a', { attrs: {}, type: 'underline' }), marked('b', underline)), '!adf:underline[a]{attrs=empty}!adf:underline[b]\n')
   assert.equal(emitted(marked('x', { attrs: { type: 'sub' }, type: 'subsup' })), '!adf:subsup[x]{type=sub}\n')
   assert.equal(emitted(marked('x', { attrs: { color: '#ae2e24' }, type: 'textColor' })), '!adf:textColor[x]{color="#ae2e24"}\n')
   assert.equal(emitted(marked('x', { attrs: { color: '#091e42', size: 2 }, type: 'border' })), '!adf:border[x]{color="#091e42" size=2}\n')
@@ -746,5 +753,5 @@ test('carries whitespace CommonMark strips in the reserved text directive', () =
 
 test("joins a mark run's segments as a walk rather than as one call's arguments", () => {
   const run = Array.from({ length: 200000 }, (): AdfNode => ({ marks: [{ type: 'strong' }], text: 'a', type: 'text' }))
-  assert.equal(markdown(adfToMarkdown(document({ content: run, type: 'paragraph' }))), `**${'a'.repeat(200000)}**\n`)
+  assert.equal(markdown(adfToMarkdown(document({ content: run, type: 'paragraph' }))), `**${Array.from({ length: 200000 }, () => 'a').join('!adf:textBreak{}')}**\n`)
 })

src/markdown/emit/adf-to-markdown.ts

@@ -1,14 +1,16 @@
 import type { AdfDocument, AdfNode } from '../../adf/document.ts'
 import type { BlockNodeModel } from '../../adf/block-nodes.ts'
-import { adfDocumentFault, carriesOnly, nodeAttrs, nodeContent, nodeMarks } from '../../adf/document.ts'
+import type { Flavour } from '../plain/conventions.ts'
-import { blockDirectiveForm, listBreakSpelling } from '../block-directive.ts'
+import { adfDocumentFault, holdsOnlyAttributes, isUnmarkedBareText, nodeAttrs, nodeContent } from '../../adf/document.ts'
+import { alertMarker, foldedAlertMarker, leadingMarker, readAlertMarker, readTaskMarker, taskMarker } from '../plain/conventions.ts'
+import { blockDirectiveForm, documentSpelling, listBreakSpelling } from '../block-directive.ts'
 import { blockNodeModel, blockNodes } from '../../adf/block-nodes.ts'
 import { carriedBlock } from '../opaque-carry.ts'
 import { emitInlineLine } from './inline-line.ts'
 import { failure, faulted, success, type ConvertErrorPath, type Result } from '../../result.ts'
 import { fencedCodeBlock } from '../commonmark/backtick-runs.ts'
 import { holdsNullCharacter, isBlankLine, isThematicBreak, markerInterruptsParagraph } from '../commonmark/grammar.ts'
-import { languageSlot } from '../code-language.ts'
+import { languageSlot, type LanguageSlot } from '../code-language.ts'
 import { largestNesting } from '../../nesting.ts'
 import { spellBlockDirectiveOpener } from './block-directive-spelling.ts'
 import { spellDirectiveCloser, spellDirectiveOpener } from '../directive-syntax.ts'
@@ -20,32 +22,38 @@ type BlockSpelling = 'commonmark' | 'directive' | 'list'
 type EmittedBlock = { headroom: number; spelling: BlockSpelling; text: string }
 type KeptSpelling = { block: EmittedBlock | undefined; depth: number }
 type PlacedBlock = Omit<EmittedBlock, 'headroom'> & { node: AdfNode }
+type PlacedBlocks = { blocks: readonly PlacedBlock[]; headroom: number }
 // Keyed by reference: only a caller building one object per position (the parse, the plain reduction) passes one; a consumer's document may share a node.
 export type SpellingMemo = Map<AdfNode, KeptSpelling>
-type Walk = { blocks: readonly PlacedBlock[]; headroom: number }
+type WalkedItem = { node: AdfNode; walk: PlacedBlocks }
-type WalkedItem = { node: AdfNode; walk: Walk }
+export type Writing = { flavour: Flavour; memo: SpellingMemo | undefined }
 
 export const largestListMarker = 999999999
 // Bare because tryList admits no item carrying attributes, marks or text.
 const listItemOpener = spellDirectiveOpener('listItem', undefined, '')
 
 export function adfToMarkdown(document: AdfDocument): Result<string> {
+  return writeMarkdown(document, 'lossless')
+}
+
+export function writeMarkdown(document: AdfDocument, flavour: Flavour): Result<string> {
   const fault = adfDocumentFault(document)
   if (fault !== undefined) return faulted(fault, [])
   if (document.version !== 1) return failure('unsupported-document-version', `no markdown spelling carries ADF version ${document.version}`, [])
-  const walk = walkBlocks(nodeContent(document), [], 0, undefined)
+  if (document.content === undefined) return success(`${documentSpelling}\n`)
+  const walk = walkBlocks(document.content, [], 0, { flavour, memo: undefined })
   if (!walk.ok) return walk
   const text = joinBlocks(walk.value.blocks, 'document')
   return success(text === '' ? '' : `${text}\n`)
 }
 
 // headroom: the least slack any depth guard below the walk has.
-function walkBlocks(nodes: readonly AdfNode[], path: ConvertErrorPath, depth: number, memo: SpellingMemo | undefined): Result<Walk> {
+function walkBlocks(nodes: readonly AdfNode[], path: ConvertErrorPath, depth: number, writing: Writing): Result<PlacedBlocks> {
   let headroom = largestNesting - depth
   if (headroom < 0) return tooDeep(path)
   const blocks: PlacedBlock[] = []
   for (const [index, node] of nodes.entries()) {
-    const block = emitBlock(node, [...path, 'content', index], depth, memo)
+    const block = emitBlock(node, [...path, 'content', index], depth, writing)
     if (!block.ok) return block
     headroom = Math.min(headroom, block.value.headroom)
     blocks.push({ ...block.value, node })
@@ -68,64 +76,133 @@ function joinBlocks(blocks: readonly PlacedBlock[], container: BlockContainer):
 }
 
 function separationBetween(previous: PlacedBlock, next: PlacedBlock, container: BlockContainer): string {
-  const plainPair = previous.spelling !== 'directive' && next.spelling !== 'directive'
+  const bothCommonMark = previous.spelling !== 'directive' && next.spelling !== 'directive'
-  if (plainPair && next.spelling === 'list') {
+  if (bothCommonMark && next.spelling === 'list') {
     if (previous.spelling === 'list' && previous.node.type === next.node.type) {
       const gap = container === 'directive' ? '\n' : '\n\n'
       return `${gap}${listBreakSpelling}${gap}`
     }
     if (container === 'list-item') return interruptsParagraph(next.node) ? '\n' : '\n\n'
   }
-  return container === 'directive' && !plainPair ? '\n' : '\n\n'
+  return container === 'directive' && !bothCommonMark ? '\n' : '\n\n'
 }
 
 function interruptsParagraph(node: AdfNode): boolean {
   const items = nodeContent(node)
-  const empty = items[0] === undefined || nodeContent(items[0]).length === 0
+  const empty = node.type !== 'taskList' && (items[0] === undefined || nodeContent(items[0]).length === 0)
   if (node.type !== 'orderedList') return markerInterruptsParagraph(undefined, empty)
   return markerInterruptsParagraph(listStart(node, items.length) ?? 0, empty)
 }
 
-function emitBlock(node: AdfNode, path: ConvertErrorPath, depth: number, memo: SpellingMemo | undefined): Result<EmittedBlock> {
+function emitBlock(node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing): Result<EmittedBlock> {
   const model = blockNodeModel(node.type)
   if (model === undefined) return commonMarkLine(carriedBlock(node, path, depth))
-  const readable = readableBlock(node, path, depth, memo)
+  const readable = readableBlock(node, path, depth, writing)
   if (readable !== undefined) return readable
-  return emitDirectiveBlock(node, model, path, depth, () => walkBlocks(nodeContent(node), path, depth + 1, memo))
+  return emitDirectiveBlock(node, model, path, depth, () => walkBlocks(nodeContent(node), path, depth + 1, writing))
 }
 
-export function commonMarkSpelling(node: AdfNode, path: ConvertErrorPath, depth: number, memo: SpellingMemo): Result<null> | undefined {
+export function commonMarkSpelling(node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing): Result<null> | undefined {
-  const readable = readableBlock(node, path, depth, memo)
+  const readable = readableBlock(node, path, depth, writing)
   if (readable === undefined) return undefined
   if (!readable.ok) return readable
   return readable.value.spelling === 'directive' ? undefined : success(null)
 }
 
-function readableBlock(node: AdfNode, path: ConvertErrorPath, depth: number, memo: SpellingMemo | undefined): Result<EmittedBlock> | undefined {
+function readableBlock(node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing): Result<EmittedBlock> | undefined {
+  const { memo } = writing
   const kept = memo?.get(node)
   if (kept !== undefined) {
     if (kept.block === undefined) return undefined
     // A read below the fill would skip the depth guards the walk it replaces runs (docs/decisions.md §The spelling memo).
     if (depth <= kept.depth) return success({ ...kept.block, headroom: kept.block.headroom + kept.depth - depth })
   }
-  const spelled = spellReadableBlock(node, path, depth, memo)
+  const spelled = spellReadableBlock(node, path, depth, writing)
   if (spelled === undefined) memo?.set(node, { block: undefined, depth })
   else if (spelled.ok) memo?.set(node, { block: spelled.value, depth })
   return spelled
 }
 
-function spellReadableBlock(node: AdfNode, path: ConvertErrorPath, depth: number, memo: SpellingMemo | undefined): Result<EmittedBlock> | undefined {
+function spellReadableBlock(node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing): Result<EmittedBlock> | undefined {
-  if (node.type === 'blockquote') return tryBlockquote(node, path, depth, memo)
+  const plain = writing.flavour === 'plain' ? spellPlainBlock(node, path, depth, writing) : undefined
-  if (node.type === 'bulletList' || node.type === 'orderedList') return tryList(node, path, depth, memo)
+  if (plain !== undefined) return plain
-  if (node.type === 'codeBlock') return tryCodeBlock(node, path)
+  if (node.type === 'blockquote') return tryBlockquote(node, path, depth, writing)
-  if (node.type === 'heading') return tryHeading(node, path)
+  if (node.type === 'bulletList' || node.type === 'orderedList') return tryList(node, path, depth, writing)
-  if (node.type === 'mediaSingle') return readableText(tryImage(node, path))
+  if (node.type === 'codeBlock') return readableText(tryCodeBlock(node))
-  if (node.type === 'paragraph') return tryParagraph(node, path)
+  if (node.type === 'heading') return tryHeading(node, path, writing.flavour)
+  if (node.type === 'mediaSingle') return readableText(tryImage(node))
+  if (node.type === 'paragraph') return tryParagraph(node, path, writing.flavour)
   if (node.type === 'rule') return readableText(tryRule(node))
-  if (node.type === 'table') return readableText(tryPipeTable(node, path))
+  if (node.type === 'table') return readableText(tryPipeTable(node, path, writing.flavour))
   return undefined
 }
 
+// The plain flavour's nodes, in the shapes the plain reduction leaves them.
+function spellPlainBlock(node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing): Result<EmittedBlock> | undefined {
+  if (node.type === 'panel') return quotedUnder(alertMarker(nodeAttrs(node)['panelType']), node, path, depth, writing)
+  if (node.type === 'taskList') return tryTaskList(node, path, depth, writing)
+  if (node.type !== 'expand' && node.type !== 'nestedExpand') return undefined
+  const title = nodeAttrs(node)['title']
+  if (typeof title !== 'string') return quotedUnder(foldedAlertMarker, node, path, depth, writing)
+  // The reader takes a title as lossless inline text.
+  const line = emitInlineLine([{ text: title, type: 'text' }], 'paragraph', path, 'lossless')
+  return line.ok ? quotedUnder(`${foldedAlertMarker} ${line.value}`, node, path, depth, writing) : line
+}
+
+function quotedUnder(head: string, node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing): Result<EmittedBlock> {
+  const inner = walkBlocks(nodeContent(node), path, depth + 1, writing)
+  if (!inner.ok) return inner
+  const body = joinBlocks(inner.value.blocks, 'document')
+  return success(commonMarkText(quoted(body === '' ? head : `${head}\n\n${body}`), inner.value.headroom))
+}
+
+function quoted(text: string): string {
+  return text
+    .split('\n')
+    .map((line) => (line === '' ? '>' : `> ${line}`))
+    .join('\n')
+}
+
+function tryTaskList(node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing): Result<EmittedBlock> {
+  const items: PlacedBlock[][] = []
+  let headroom = largestNesting - depth - 1
+  // A child other than a task nests in the task before it.
+  for (const [index, child] of nodeContent(node).entries()) {
+    const task = child.type === 'taskItem' || child.type === 'blockTaskItem'
+    const walk = task ? taskBlocks(child, [...path, 'content', index], depth + 1, writing) : placedBlock(child, [...path, 'content', index], depth + 1, writing)
+    if (!walk.ok) return walk
+    headroom = Math.min(headroom, walk.value.headroom)
+    const previous = items.at(-1)
+    if (task || previous === undefined) items.push([...walk.value.blocks])
+    else for (const block of walk.value.blocks) previous.push(block)
+  }
+  const lines = items.map((blocks) => tryListItemLines(joinBlocks(blocks, 'list-item'), '- '))
+  // The plain reduction leaves no task a list item cannot hold: a directive here would break the flavour.
+  return lines.includes(undefined) ? failure('unsupported-node-shape', 'a task holds blocks no list item spells', path) : success({ headroom, spelling: 'list', text: lines.join('\n') })
+}
+
+function placedBlock(node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing): Result<PlacedBlocks> {
+  const block = emitBlock(node, path, depth, writing)
+  return block.ok ? success({ blocks: [{ ...block.value, node }], headroom: block.value.headroom }) : block
+}
+
+// The marker leads the first paragraph, or stands as one where the blocks open with another.
+function taskBlocks(task: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing): Result<PlacedBlocks> {
+  const marker = taskMarker(nodeAttrs(task)['state'])
+  const markerBlock: PlacedBlock = { node: { type: 'paragraph' }, spelling: 'commonmark', text: marker }
+  if (task.type === 'taskItem') {
+    const content = nodeContent(task)
+    const line = content.length === 0 ? success('') : emitInlineLine(content, 'paragraph', path, writing.flavour)
+    if (!line.ok) return line
+    return success({ blocks: [{ ...markerBlock, text: line.value === '' ? marker : `${marker} ${line.value}` }], headroom: Number.POSITIVE_INFINITY })
+  }
+  const walk = walkBlocks(nodeContent(task), path, depth, writing)
+  if (!walk.ok) return walk
+  const [first, ...rest] = walk.value.blocks
+  const blocks = first?.node.type === 'paragraph' ? [{ ...first, text: `${marker} ${first.text}` }, ...rest] : [markerBlock, ...walk.value.blocks]
+  return success({ blocks, headroom: walk.value.headroom })
+}
+
 function readableText(text: string | undefined): Result<EmittedBlock> | undefined {
   return text === undefined ? undefined : success(commonMarkText(text))
 }
@@ -143,7 +220,7 @@ function directivePair(node: AdfNode, opener: string, body: string, headroom: nu
   return { headroom, spelling: 'directive', text: `${opener}\n${body === '' ? '' : `${body}\n`}${spellDirectiveCloser(node.type)}` }
 }
 
-function emitDirectiveBlock(node: AdfNode, model: BlockNodeModel, path: ConvertErrorPath, depth: number, walkBody: () => Result<Walk>): Result<EmittedBlock> {
+function emitDirectiveBlock(node: AdfNode, model: BlockNodeModel, path: ConvertErrorPath, depth: number, walkBody: () => Result<PlacedBlocks>): Result<EmittedBlock> {
   if (node.text !== undefined) return failure('unsupported-node-shape', `a ${node.type} carries no text: this one holds text`, path)
   if (blockDirectiveForm(node.type) === 'leaf' && nodeContent(node).length > 0) return failure('unsupported-node-shape', `a ${node.type} holds no content: this one holds some`, path)
   if (model.contentModel === 'code') return emitCodeDirective(node, model, path, depth)
@@ -153,10 +230,10 @@ function emitDirectiveBlock(node: AdfNode, model: BlockNodeModel, path: ConvertE
   return emitDirectiveBody(node, model, opener.value, path, walkBody)
 }
 
-function emitDirectiveBody(node: AdfNode, model: BlockNodeModel, opener: string, path: ConvertErrorPath, walkBody: () => Result<Walk>): Result<EmittedBlock> {
+function emitDirectiveBody(node: AdfNode, model: BlockNodeModel, opener: string, path: ConvertErrorPath, walkBody: () => Result<PlacedBlocks>): Result<EmittedBlock> {
   if (blockDirectiveForm(node.type) === 'leaf') return success({ headroom: Number.POSITIVE_INFINITY, spelling: 'directive', text: opener })
   if (model.contentModel === 'inline') {
-    const line = emitInlineLine(nodeContent(node), 'paragraph', path)
+    const line = emitInlineLine(nodeContent(node), 'paragraph', path, 'lossless')
     if (!line.ok) return line
     return success(directivePair(node, opener, line.value))
   }
@@ -165,87 +242,80 @@ function emitDirectiveBody(node: AdfNode, model: BlockNodeModel, opener: string,
   return success(directivePair(node, opener, joinBlocks(walk.value.blocks, 'directive'), walk.value.headroom))
 }
 
-function tryBlockquote(node: AdfNode, path: ConvertErrorPath, depth: number, memo: SpellingMemo | undefined): Result<EmittedBlock> | undefined {
+function tryBlockquote(node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing): Result<EmittedBlock> | undefined {
-  if (!carriesOnly(node, [])) return undefined
+  if (!holdsOnlyAttributes(node, [])) return undefined
-  const inner = walkBlocks(nodeContent(node), path, depth + 1, memo)
+  const inner = walkBlocks(nodeContent(node), path, depth + 1, writing)
   if (!inner.ok) return inner
   const text = joinBlocks(inner.value.blocks, 'document')
-    .split('\n')
+  const alert = writing.flavour === 'plain' && leadingMarker(text, readAlertMarker) !== undefined
-    .map((line) => (line === '' ? '>' : `> ${line}`))
+  return success(commonMarkText(quoted(alert ? `\\${text}` : text), inner.value.headroom))
-    .join('\n')
-  return success(commonMarkText(text, inner.value.headroom))
 }
 
-function tryCodeBlock(node: AdfNode, path: ConvertErrorPath): Result<EmittedBlock> | undefined {
+function tryCodeBlock(node: AdfNode): string | undefined {
-  if (!carriesOnly(node, ['language'])) return undefined
+  if (!holdsOnlyAttributes(node, ['language'])) return undefined
   const slot = languageSlot(nodeAttrs(node)['language'])
   if (slot.kind === 'attribute') return undefined
-  const text = codeBlockText(node, path)
+  const [only, ...others] = fencedTexts(node) ?? []
-  if (!text.ok) return text
+  if (only === undefined || others.length > 0) return undefined
-  return success(commonMarkText(fencedCodeBlock(slot.kind === 'fence' ? slot.info : '', text.value)))
+  return fencedCodeBlock(slot.kind === 'fence' ? slot.info : '', only)
 }
 
+// spec/flavour.md, The CommonMark blocks: one fence per text node, the language on each; with no fence to carry it, the attribute does.
 function emitCodeDirective(node: AdfNode, model: BlockNodeModel, path: ConvertErrorPath, depth: number): Result<EmittedBlock> {
-  const slot = languageSlot(nodeAttrs(node)['language'])
+  const texts = fencedTexts(node)
+  if (texts === undefined) return commonMarkLine(carriedBlock(node, path, depth))
+  const slot: LanguageSlot = texts.length === 0 ? { kind: 'attribute' } : languageSlot(nodeAttrs(node)['language'])
   const opener = spellBlockDirectiveOpener(node, model, path, slot.kind === 'attribute' ? [] : ['language'])
   if (opener === undefined) return commonMarkLine(carriedBlock(node, path, depth))
   if (!opener.ok) return opener
-  const text = codeBlockText(node, path)
+  const info = slot.kind === 'fence' ? slot.info : ''
-  if (!text.ok) return text
+  return success(directivePair(node, opener.value, texts.map((text) => fencedCodeBlock(info, text)).join('\n')))
-  return success(directivePair(node, opener.value, fencedCodeBlock(slot.kind === 'fence' ? slot.info : '', text.value)))
 }
 
-function codeBlockText(node: AdfNode, path: ConvertErrorPath): Result<string> {
+// The text of each fence, or `undefined` where a child holds what no fence keeps, so the block carry takes the node.
-  let text = ''
+function fencedTexts(node: AdfNode): string[] | undefined {
-  for (const [index, child] of nodeContent(node).entries()) {
+  if (node.content === undefined) return ['']
-    const childPath = [...path, 'content', index]
+  const texts: string[] = []
-    if (
+  for (const child of node.content) {
-      child.type !== 'text' ||
+    if (!isUnmarkedBareText(child) || typeof child.text !== 'string' || child.text === '' || /\r/.test(child.text) || holdsNullCharacter(child.text)) return undefined
-      typeof child.text !== 'string' ||
+    texts.push(child.text)
-      child.text === '' ||
-      nodeContent(child).length > 0 ||
-      nodeMarks(child).length > 0 ||
-      Object.keys(nodeAttrs(child)).length > 0
-    ) {
-      return failure('unsupported-node-shape', `a codeBlock holds plain text nodes only: this ${child.type} node is not one`, childPath)
-    }
-    if (/\r/.test(child.text)) return failure('unspellable-character', 'a codeBlock holds no carriage return CommonMark keeps: this text holds one', childPath)
-    if (holdsNullCharacter(child.text)) return failure('unspellable-character', 'a codeBlock holds a null character CommonMark replaces', childPath)
-    text += child.text
   }
-  return success(text)
+  return texts
 }
 
-function tryHeading(node: AdfNode, path: ConvertErrorPath): Result<EmittedBlock> | undefined {
+function tryHeading(node: AdfNode, path: ConvertErrorPath, flavour: Flavour): Result<EmittedBlock> | undefined {
-  if (!carriesOnly(node, ['level'])) return undefined
+  if (!holdsOnlyAttributes(node, ['level'])) return undefined
   const level = nodeAttrs(node)['level']
   if (typeof level !== 'number' || !Number.isInteger(level) || level < 1 || level > 6) return undefined
   const hashes = '#'.repeat(level)
   const content = nodeContent(node)
   if (content.length === 0) return success(commonMarkText(hashes))
-  const line = emitInlineLine(content, 'heading', path)
+  const line = emitInlineLine(content, 'heading', path, flavour)
   if (!line.ok) return line
   return success(commonMarkText(`${hashes} ${line.value}`))
 }
 
-function tryList(node: AdfNode, path: ConvertErrorPath, depth: number, memo: SpellingMemo | undefined): Result<EmittedBlock> | undefined {
+function tryList(node: AdfNode, path: ConvertErrorPath, depth: number, writing: Writing): Result<EmittedBlock> | undefined {
   const ordered = node.type === 'orderedList'
-  if (!carriesOnly(node, ordered ? ['order'] : [])) return undefined
+  if (!holdsOnlyAttributes(node, ordered ? ['order'] : [])) return undefined
   const items = nodeContent(node)
   const start = listStart(node, items.length)
   if (start === undefined || items.length === 0) return undefined
-  if (items.some((item) => item.type !== 'listItem' || !carriesOnly(item, []))) return undefined
+  if (items.some((item) => item.type !== 'listItem' || !holdsOnlyAttributes(item, []))) return undefined
   const walked: WalkedItem[] = []
   let headroom = Number.POSITIVE_INFINITY
   for (const [offset, item] of items.entries()) {
-    const walk = walkBlocks(nodeContent(item), [...path, 'content', offset], depth + 1, memo)
+    const walk = walkBlocks(nodeContent(item), [...path, 'content', offset], depth + 1, writing)
     if (!walk.ok) return walk
     headroom = Math.min(headroom, walk.value.headroom)
     walked.push({ node: item, walk: walk.value })
   }
   const lines: string[] = []
   for (const [offset, item] of walked.entries()) {
-    const line = tryListItemLines(item.walk.blocks, ordered ? `${start + offset}. ` : '- ')
+    const inner = joinBlocks(item.walk.blocks, 'list-item')
+    // GitHub reads a task marker opening any item's first paragraph as a checkbox, whatever its siblings hold.
+    const escaped = writing.flavour === 'plain' && leadingMarker(inner, readTaskMarker) !== undefined ? `\\${inner}` : inner
+    const line = tryListItemLines(escaped, ordered ? `${start + offset}. ` : '- ')
     if (line === undefined) {
       // The directive form spends a level the walk did not count.
       if (headroom < 1) return tooDeep(path)
@@ -263,12 +333,11 @@ function directiveItems(items: readonly WalkedItem[]): PlacedBlock[] {
 function listStart(node: AdfNode, items: number): number | undefined {
   if (node.type !== 'orderedList') return 0
   const start = nodeAttrs(node)['order']
-  if (typeof start !== 'number' || !Number.isInteger(start) || start < 0 || start > largestListMarker) return undefined
+  if (typeof start !== 'number' || !Number.isInteger(start) || start < 0 || Object.is(start, -0) || start > largestListMarker) return undefined
   return start + items - 1 > largestListMarker ? undefined : start
 }
 
-function tryListItemLines(blocks: readonly PlacedBlock[], marker: string): string | undefined {
+function tryListItemLines(inner: string, marker: string): string | undefined {
-  const inner = joinBlocks(blocks, 'list-item')
   if (inner === '') return marker.trimEnd()
   const body = inner.split('\n')
   if (body.some((line) => line !== '' && isBlankLine(line))) return undefined
@@ -278,15 +347,15 @@ function tryListItemLines(blocks: readonly PlacedBlock[], marker: string): strin
   return lines.join('\n')
 }
 
-function tryParagraph(node: AdfNode, path: ConvertErrorPath): Result<EmittedBlock> | undefined {
+function tryParagraph(node: AdfNode, path: ConvertErrorPath, flavour: Flavour): Result<EmittedBlock> | undefined {
   const content = nodeContent(node)
-  if (content.length === 0 || !carriesOnly(node, [])) return undefined
+  if (content.length === 0 || !holdsOnlyAttributes(node, [])) return undefined
-  const line = emitInlineLine(content, 'paragraph', path)
+  const line = emitInlineLine(content, 'paragraph', path, flavour)
   if (!line.ok) return line
   return success(commonMarkText(line.value))
 }
 
 function tryRule(node: AdfNode): string | undefined {
-  if (!carriesOnly(node, []) || nodeContent(node).length > 0) return undefined
+  if (!holdsOnlyAttributes(node, []) || nodeContent(node).length > 0) return undefined
   return '---'
 }

src/markdown/emit/block-directive-spelling.ts

@@ -5,6 +5,7 @@ import { blockArgument, markValues, marksAttribute } from '../block-directive.ts
 import { failure, success, type ConvertErrorPath, type Result } from '../../result.ts'
 import { isBareToken, spellAttributes, spellDirectiveOpener, spellJsonAttribute, spellVocabulary } from '../directive-syntax.ts'
 import { overNested } from '../../json-value.ts'
+import { spellEmptyKeys } from '../empty-keys.ts'
 import { vocabularyPairs } from '../../adf/attribute-vocabulary.ts'
 
 export function spellBlockDirectiveOpener(node: AdfNode, model: BlockNodeModel, path: ConvertErrorPath, spelledByBody: readonly string[] = []): Result<string> | undefined {
@@ -14,7 +15,7 @@ export function spellBlockDirectiveOpener(node: AdfNode, model: BlockNodeModel,
   const spelled = argumentAttribute === undefined ? spelledByBody : [argumentAttribute, ...spelledByBody]
   const pairs = vocabularyPairs(nodeAttrs(node), model.attributes, spelled)
   if (pairs === undefined) return undefined
-  const spelledPairs = spellVocabulary(pairs)
+  const spelledPairs = [...spellVocabulary(pairs), ...spellEmptyKeys(node)]
   const marks = nodeMarks(node)
   if (marks.length > 0) {
     const values = markValues(marks)

src/markdown/emit/image.ts

@@ -1,23 +1,22 @@
 import type { AdfNode } from '../../adf/document.ts'
-import type { ConvertErrorPath } from '../../result.ts'
+import { holdsOnlyAttributes, nodeAttrs, nodeContent } from '../../adf/document.ts'
-import { carriesOnly, nodeAttrs, nodeContent } from '../../adf/document.ts'
 import { serializeCanonicalJson } from '../../canonical-json.ts'
 import { tryImageLine } from './inline-line.ts'
 
 const centeredMediaSingle = '{"layout":"center"}'
 const imageAttributes = ['alt', 'type', 'url']
 
-export function tryImage(node: AdfNode, path: ConvertErrorPath): string | undefined {
+export function tryImage(node: AdfNode): string | undefined {
   const image = imageShape(node)
   if (image === undefined) return undefined
-  return tryImageLine(image.alt, image.url, [...path, 'content', 0])
+  return tryImageLine(image.alt, image.url)
 }
 
 function imageShape(node: AdfNode): { alt: string | undefined; url: string } | undefined {
   const content = nodeContent(node)
   const media = content[0]
-  if (!carriesOnly(node, ['layout']) || serializeCanonicalJson(nodeAttrs(node), 'compact') !== centeredMediaSingle) return undefined
+  if (!holdsOnlyAttributes(node, ['layout']) || serializeCanonicalJson(nodeAttrs(node), 'compact') !== centeredMediaSingle) return undefined
-  if (media === undefined || content.length !== 1 || media.type !== 'media' || !carriesOnly(media, imageAttributes) || nodeContent(media).length > 0) return undefined
+  if (media === undefined || content.length !== 1 || media.type !== 'media' || !holdsOnlyAttributes(media, imageAttributes) || nodeContent(media).length > 0) return undefined
   const attrs = nodeAttrs(media)
   const alt = attrs['alt']
   const url = attrs['url']

src/markdown/emit/inline-directive-spelling.ts

@@ -2,9 +2,10 @@ import type { AdfNode } from '../../adf/document.ts'
 import type { InlineNodeModel } from '../../adf/inline-nodes.ts'
 import { nodeAttrs } from '../../adf/document.ts'
 import { spellAttributes, spellVocabulary } from '../directive-syntax.ts'
+import { spellEmptyKeys } from '../empty-keys.ts'
 import { vocabularyPairs } from '../../adf/attribute-vocabulary.ts'
 
 export function spellInlineNodeAttributes(node: AdfNode, model: InlineNodeModel): string | undefined {
   const pairs = vocabularyPairs(nodeAttrs(node), model.attributes, model.textAttribute === undefined ? [] : [model.textAttribute])
-  return pairs === undefined ? undefined : spellAttributes(spellVocabulary(pairs))
+  return pairs === undefined ? undefined : spellAttributes([...spellVocabulary(pairs), ...spellEmptyKeys(node)])
 }

src/markdown/emit/inline-line.ts

@@ -1,18 +1,20 @@
 import type { AdfMark, AdfNode } from '../../adf/document.ts'
+import type { Flavour } from '../plain/conventions.ts'
 import type { InlineNodeModel } from '../../adf/inline-nodes.ts'
 import type { LineContainer } from '../line-container.ts'
 import { assembleInlineLine, isSyntax, type InlineEscaping, type InlineSegment, type MarkRun, type NodeRange } from './line-escaping.ts'
 import { carriedInline } from '../opaque-carry.ts'
-import { claimsLine, holdsNullCharacter, trimTrailingSpace } from '../commonmark/grammar.ts'
+import { holdsNullCharacter, trimTrailingSpace } from '../commonmark/grammar.ts'
 import { commonMarkLink, linkHref, markSpelling, spellMarkAttributes } from '../mark-spellings.ts'
 import { escapeUnbalanced, spellDestination } from '../commonmark/link-syntax.ts'
-import { failure, faulted, success, type ConvertErrorPath, type Result } from '../../result.ts'
+import { identicalMark, isBareText, nodeAttrs, nodeContent, nodeMarks } from '../../adf/document.ts'
+import { failure, success, type ConvertErrorPath, type Result } from '../../result.ts'
+import { highlightDelimiter } from '../plain/conventions.ts'
 import { inlineNodeModel } from '../../adf/inline-nodes.ts'
+import { joinsWhenRead, textBreakSpelling } from '../adjacent-text.ts'
 import { largestNesting } from '../../nesting.ts'
 import { longestBacktickRun } from '../commonmark/backtick-runs.ts'
-import { nodeAttrs, nodeContent, nodeMarks } from '../../adf/document.ts'
+import { slotFault, spellInlineDirectiveOpener, spellInlineLeafDirective } from '../directive-syntax.ts'
-import { sameMark } from '../../adf/editor-normal.ts'
-import { slotLineEndingFault, spellInlineDirectiveOpener, spellInlineLeafDirective } from '../directive-syntax.ts'
 import { spellInlineNodeAttributes } from './inline-directive-spelling.ts'
 import { spellTextDirective } from '../text-directive.ts'
 
@@ -24,6 +26,7 @@ type InlineContext = {
   atBlockEnd: boolean
   bracketed: boolean
   carried: ReadonlySet<number>
+  flavour: Flavour
   openingLinkAsDirective: boolean
   path: ConvertErrorPath
   spansLines: boolean
@@ -33,48 +36,47 @@ type InlineRun = { index: number; kind: 'marked'; mark: AdfMark; nodes: AdfNode[
 
 type LineAttempt = { fallback: NodeRange | 'opening-link'; line?: undefined } | { fallback?: undefined; line: string }
 
-type LineFallbacks = { carried: Set<number>; openingLinkAsDirective: boolean }
+type LineFallbacks = { carried: Set<number>; flavour: Flavour; openingLinkAsDirective: boolean }
 
-export type PlainLineFallback = { kind: 'claimed-line'; line: number; text: string } | { kind: 'opening-link' } | { kind: 'unspellable-run'; run: MarkRun }
+export type PlainLineFallback = { kind: 'opening-link' } | { kind: 'unspellable-run'; runs: [MarkRun, ...MarkRun[]] }
 
-export function emitInlineLine(nodes: readonly AdfNode[], container: LineContainer, path: ConvertErrorPath): Result<string> {
+export function emitInlineLine(nodes: readonly AdfNode[], container: LineContainer, path: ConvertErrorPath, flavour: Flavour): Result<string> {
-  const emitted = emitLine(nodes, container, path)
+  const emitted = emitLine(nodes, container, path, flavour)
   if (!emitted.ok) return emitted
   return success(emitted.value.line)
 }
 
 export function openingLinkTakesDirective(nodes: readonly AdfNode[], path: ConvertErrorPath): Result<boolean> {
-  const emitted = emitLine(nodes, 'paragraph', path)
+  const emitted = emitLine(nodes, 'paragraph', path, 'lossless')
   if (!emitted.ok) return emitted
   return success(emitted.value.openingLinkAsDirective)
 }
 
 export function plainLineFallback(nodes: readonly AdfNode[], container: LineContainer, path: ConvertErrorPath): Result<PlainLineFallback | undefined> {
-  const emission = lineSegments(nodes, container, path, { carried: new Set(), openingLinkAsDirective: false })
+  const emission = lineSegments(nodes, container, path, { carried: new Set(), flavour: 'plain', openingLinkAsDirective: false })
   if (!emission.ok) return emission
   if (emission.value.carry !== undefined) return failure('unsupported-node-shape', 'an inline node on a plain line has no spelling but the carry', path)
-  const verdict = lineVerdict(emission.value.segments, container)
+  const verdict = lineVerdict(emission.value.segments, container, 'plain')
   return success(verdict.kind === 'line' ? undefined : verdict)
 }
 
-export function tryPipeCell(nodes: readonly AdfNode[], path: ConvertErrorPath): string | undefined {
+export function tryPipeCell(nodes: readonly AdfNode[], path: ConvertErrorPath, flavour: Flavour): string | undefined {
-  const emitted = emitLine(nodes, 'table-cell', path)
+  const emitted = emitLine(nodes, 'table-cell', path, flavour)
   if (!emitted.ok) return undefined
   if (emitted.value.segments.some((segment) => isSyntax(segment.escaping) && segment.text.includes('|'))) return undefined
   return emitted.value.line
 }
 
-export function tryImageLine(alt: string | undefined, href: string, path: ConvertErrorPath): string | undefined {
+export function tryImageLine(alt: string | undefined, href: string): string | undefined {
   if (alt !== undefined && (/^[ \t]|[ \t]$|[\n\r]/.test(alt) || holdsNullCharacter(alt))) return undefined
   const destination = spellDestination(href)
   if (destination === undefined) return undefined
   const description: InlineSegment[] = alt === undefined ? [] : [{ escaping: 'bracketed', text: alt }]
-  const attempt = attemptLine([syntax('!['), ...description, syntax(`](${destination})`)], 'paragraph', path)
+  return attemptLine([syntax('!['), ...description, syntax(`](${destination})`)], 'paragraph', 'lossless').line
-  return attempt.ok ? attempt.value.line : undefined
 }
 
-function emitLine(nodes: readonly AdfNode[], container: LineContainer, path: ConvertErrorPath): Result<EmittedLine> {
+function emitLine(nodes: readonly AdfNode[], container: LineContainer, path: ConvertErrorPath, flavour: Flavour): Result<EmittedLine> {
-  const fallbacks: LineFallbacks = { carried: new Set(), openingLinkAsDirective: false }
+  const fallbacks: LineFallbacks = { carried: new Set(), flavour, openingLinkAsDirective: false }
   // Terminates because takeFallback refuses a pass that took no new fallback.
   for (;;) {
     const emission = lineSegments(nodes, container, path, fallbacks)
@@ -84,12 +86,11 @@ function emitLine(nodes: readonly AdfNode[], container: LineContainer, path: Con
       if (!taken.ok) return taken
       continue
     }
-    const attempt = attemptLine(emission.value.segments, container, path)
+    const attempt = attemptLine(emission.value.segments, container, flavour)
-    if (!attempt.ok) return attempt
+    if (attempt.line !== undefined) {
-    if (attempt.value.line !== undefined) {
+      return success({ line: attempt.line, openingLinkAsDirective: fallbacks.openingLinkAsDirective, segments: emission.value.segments })
-      return success({ line: attempt.value.line, openingLinkAsDirective: fallbacks.openingLinkAsDirective, segments: emission.value.segments })
     }
-    const taken = takeFallback(fallbacks, attempt.value.fallback, path)
+    const taken = takeFallback(fallbacks, attempt.fallback, path)
     if (!taken.ok) return taken
   }
 }
@@ -111,54 +112,51 @@ function lineSegments(nodes: readonly AdfNode[], container: LineContainer, path:
   const emission = emitRun(nodes, 0, 0, context)
   if (!emission.ok) return emission
   if (emission.value.carry !== undefined) return emission
-  return success({ segments: carryStrippedWhitespace(emission.value.segments) })
+  return success({ segments: spellEdgeWhitespace(emission.value.segments) })
 }
 
-function attemptLine(segments: readonly InlineSegment[], container: LineContainer, path: ConvertErrorPath): Result<LineAttempt> {
+function attemptLine(segments: readonly InlineSegment[], container: LineContainer, flavour: Flavour): LineAttempt {
-  const verdict = lineVerdict(segments, container)
+  const verdict = lineVerdict(segments, container, flavour)
-  if (verdict.kind === 'opening-link') return success({ fallback: 'opening-link' })
+  if (verdict.kind === 'opening-link') return { fallback: 'opening-link' }
-  if (verdict.kind === 'unspellable-run') return success({ fallback: verdict.run })
+  if (verdict.kind === 'unspellable-run') return { fallback: verdict.runs[0] }
-  if (verdict.kind === 'claimed-line') return failure('unspellable-line-start', `block parsing would claim the emitted line ${JSON.stringify(verdict.text)}`, path)
+  return { line: verdict.text }
-  return success({ line: verdict.text })
 }
 
 // The fallbacks in the order a line takes them, or the line where it takes none.
-function lineVerdict(segments: readonly InlineSegment[], container: LineContainer): PlainLineFallback | { kind: 'line'; text: string } {
+function lineVerdict(segments: readonly InlineSegment[], container: LineContainer, flavour: Flavour): PlainLineFallback | { kind: 'line'; text: string } {
-  const assembled = assembleInlineLine(segments, container)
+  const assembled = assembleInlineLine(segments, container, flavour)
   if (assembled.openingLinkAsDirective) return { kind: 'opening-link' }
-  if (assembled.unspellableRun !== undefined) return { kind: 'unspellable-run', run: assembled.unspellableRun }
+  const [run, ...others] = assembled.unspellableRuns
-  const lines = assembled.line.split('\n')
+  return run === undefined ? { kind: 'line', text: assembled.line } : { kind: 'unspellable-run', runs: [run, ...others] }
-  const claimed = container === 'paragraph' ? lines.findIndex((single, index) => claimsLine(single, index === 0 ? 'first' : 'later')) : -1
-  return claimed === -1 ? { kind: 'line', text: assembled.line } : { kind: 'claimed-line', line: claimed, text: lines[claimed] ?? '' }
 }
 
 // spec/flavour.md, Inline nodes.
-function carryStrippedWhitespace(segments: readonly InlineSegment[]): InlineSegment[] {
+function spellEdgeWhitespace(segments: readonly InlineSegment[]): InlineSegment[] {
-  const carried: InlineSegment[] = []
+  const spelled: InlineSegment[] = []
   for (const [index, segment] of segments.entries()) {
     const previous = segments[index - 1]
     const next = segments[index + 1]
     const leading = previous === undefined || previous.text.includes('\n')
     const trailing = next === undefined || next.text.includes('\n')
-    carried.push(...carryEdges(segment, leading, trailing))
+    spelled.push(...edgeWhitespaceSegments(segment, leading, trailing))
   }
-  return carried
+  return spelled
 }
 
-function carryEdges(segment: InlineSegment, leading: boolean, trailing: boolean): InlineSegment[] {
+function edgeWhitespaceSegments(segment: InlineSegment, leading: boolean, trailing: boolean): InlineSegment[] {
   if (segment.escaping !== 'backslash' && segment.escaping !== 'bracketed') return [segment]
   const head = leading ? (/^[ \t]+/.exec(segment.text)?.[0] ?? '') : ''
   const body = segment.text.slice(head.length)
   const middle = trailing ? trimTrailingSpace(body) : body
   const tail = body.slice(middle.length)
   const edges: InlineSegment[] = []
-  if (head !== '') edges.push(carriedText(head))
+  if (head !== '') edges.push(textDirectiveSegment(head))
   if (middle !== '') edges.push({ escaping: segment.escaping, text: middle })
-  if (tail !== '') edges.push(carriedText(tail))
+  if (tail !== '') edges.push(textDirectiveSegment(tail))
   return edges
 }
 
-function carriedText(text: string): InlineSegment {
+function textDirectiveSegment(text: string): InlineSegment {
   return syntax(spellTextDirective(text))
 }
 
@@ -182,6 +180,7 @@ function emitRun(nodes: readonly AdfNode[], depth: number, firstIndex: number, c
   const runs = inlineRuns(nodes, depth, firstIndex, context.carried)
   const segments: InlineSegment[] = []
   for (const [offset, run] of runs.entries()) {
+    if (takesTextBreak(runs[offset - 1], run, context.carried)) segments.push(syntax(textBreakSpelling))
     const runContext = { ...context, atBlockEnd: context.atBlockEnd && offset === runs.length - 1 }
     const emitted = run.kind === 'plain' ? emitLeaf(run.node, runContext, run.index) : emitMarkedRun(run.nodes, run.mark, depth, run.index, runContext)
     if (!emitted.ok) return emitted
@@ -202,19 +201,30 @@ function inlineRuns(nodes: readonly AdfNode[], depth: number, firstIndex: number
       continue
     }
     const previous = runs[runs.length - 1]
-    if (previous?.kind === 'marked' && sameMark(previous.mark, mark)) previous.nodes.push(node)
+    if (previous?.kind === 'marked' && identicalMark(previous.mark, mark)) previous.nodes.push(node)
     else runs.push({ index, kind: 'marked', mark, nodes: [node] })
   }
   return runs
 }
 
+function takesTextBreak(previous: InlineRun | undefined, run: InlineRun, carried: ReadonlySet<number>): boolean {
+  if (previous?.kind !== 'plain' || run.kind !== 'plain') return false
+  if (carries(previous.node, carried, previous.index) || carries(run.node, carried, run.index)) return false
+  return joinsWhenRead(previous.node, run.node)
+}
+
 function nodePath(context: InlineContext, index: number): ConvertErrorPath {
   return [...context.path, 'content', index]
 }
 
+// Decides the text-node and slot-fault carries up front, so a line holding many of them is emitted once.
 function carries(node: AdfNode, carried: ReadonlySet<number>, index: number): boolean {
   if (carried.has(index)) return true
-  return node.type !== 'text' && inlineNodeModel(node.type) === undefined
+  if (node.type === 'text') return !isBareText(node) || typeof node.text !== 'string' || node.text === ''
+  const model = inlineNodeModel(node.type)
+  if (model === undefined) return true
+  const slot = model.textAttribute === undefined ? undefined : nodeAttrs(node)[model.textAttribute]
+  return typeof slot === 'string' && slotFault(node.type, slot) !== undefined && nodeContent(node).length === 0 && node.text === undefined
 }
 
 function emitLeaf(node: AdfNode, context: InlineContext, index: number): Result<Emission> {
@@ -227,7 +237,7 @@ function emitLeaf(node: AdfNode, context: InlineContext, index: number): Result<
   const types = nodeMarks(node).map((mark) => mark.type)
   if (new Set(types).size !== types.length) return failure('unsupported-node-shape', `a ${node.type} node carries one mark type twice`, path)
   const model = inlineNodeModel(node.type)
-  if (model === undefined) return emitText(node, context, index, path)
+  if (model === undefined) return success(emitText(node, context, index))
   if (node.type === 'hardBreak') return emitHardBreak(node, model, context, index, path)
   return emitInlineDirective(node, model, index, path)
 }
@@ -248,33 +258,27 @@ function emitInlineDirective(node: AdfNode, model: InlineNodeModel, index: numbe
   if (attributes === undefined) return success({ carry: { first: index, last: index } })
   const slot = model.textAttribute === undefined ? undefined : nodeAttrs(node)[model.textAttribute]
   if (slot === undefined) return success({ segments: [syntax(spellInlineLeafDirective(node.type, attributes))] })
-  if (typeof slot !== 'string') return success({ carry: { first: index, last: index } })
+  if (typeof slot !== 'string' || slotFault(node.type, slot) !== undefined) return success({ carry: { first: index, last: index } })
-  const spans = slotLineEndingFault(node.type, slot)
-  if (spans !== undefined) return faulted(spans, path)
-  if (holdsNullCharacter(slot)) return failure('unspellable-character', `a ${node.type} content slot holds a null character CommonMark replaces`, path)
   const content: InlineSegment[] = slot === '' ? [] : [{ escaping: 'bracketed', text: slot }]
   return success({ segments: [syntax(spellInlineDirectiveOpener(node.type)), ...content, syntax(`]${attributes}`)] })
 }
 
-function emitText(node: AdfNode, context: InlineContext, index: number, path: ConvertErrorPath): Result<Emission> {
+// spec/flavour.md, Text CommonMark cannot hold plainly.
-  if (Object.keys(nodeAttrs(node)).length > 0) return success({ carry: { first: index, last: index } })
+function emitText(node: AdfNode, context: InlineContext, index: number): Emission {
-  if (typeof node.text !== 'string' || node.text === '') return failure('unsupported-node-shape', 'a text node holds text: this one has none', path)
+  if (!isBareText(node) || typeof node.text !== 'string' || node.text === '') return { carry: { first: index, last: index } }
-  if (nodeContent(node).length > 0) return failure('unsupported-node-shape', 'a text node holds no content: this one holds some', path)
-  if (/\r/.test(node.text)) return failure('unspellable-character', 'a text node holds a carriage return CommonMark rewrites', path)
-  if (holdsNullCharacter(node.text)) return failure('unspellable-character', 'a text node holds a null character CommonMark replaces', path)
   const escaping: InlineEscaping = context.bracketed ? 'bracketed' : 'backslash'
-  const parts = node.text.split(/(\n+)/).filter((part) => part !== '')
+  const parts = node.text.split(/(\n+|\0+|\r)/).filter((part) => part !== '')
-  return success({ segments: parts.map((part) => (part.startsWith('\n') ? carriedText(part) : { escaping, text: part })) })
+  return { segments: parts.map((part) => (part === '\r' ? syntax('&#13;') : /^[\n\0]/.test(part) ? textDirectiveSegment(part) : { escaping, text: part })) }
 }
 
 function emitMarkedRun(nodes: readonly AdfNode[], mark: AdfMark, depth: number, index: number, context: InlineContext): Result<Emission> {
-  const path = nodePath(context, index)
   const range: NodeRange = { first: index, last: index + nodes.length - 1 }
+  if (mark.type === 'backgroundColor' && context.flavour === 'plain') return emitHighlight(nodes, depth, range, context)
   const spelling = markSpelling(mark.type)
   if (spelling === undefined) return success({ carry: range })
-  const attributes = spellMarkAttributes(mark, spelling.attributes)
+  const attributes = spellMarkAttributes(mark, spelling)
   if (attributes === undefined) return success({ carry: range })
-  if (spelling.kind === 'code') return emitCodeSpan(nodes, depth, range, path)
+  if (spelling.kind === 'code') return success(emitCodeSpan(nodes, depth, range))
   if (spelling.kind === 'emphasis') return emitEmphasis(nodes, spelling.spelling, depth, range, context)
   const link = spelling.kind === 'link' ? tryLink(nodes, mark, depth, range, context) : undefined
   if (link !== undefined) return link
@@ -288,29 +292,35 @@ function emitEmphasis(nodes: readonly AdfNode[], spelling: string, depth: number
   const inner = emitRun(nodes, depth + 1, range.first, context)
   if (!inner.ok) return inner
   if (inner.value.carry !== undefined) return inner
-  const carried = carryStrippedWhitespace(inner.value.segments)
+  const spelled = spellEdgeWhitespace(inner.value.segments)
   return success({
     segments: [
       { emphasis: 'open', escaping: 'none', nodes: { ...range, depth }, text: spelling },
-      ...carried,
+      ...spelled,
       { emphasis: 'close', escaping: 'none', nodes: { ...range, depth }, text: spelling },
     ],
   })
 }
 
-function emitCodeSpan(nodes: readonly AdfNode[], depth: number, range: NodeRange, path: ConvertErrorPath): Result<Emission> {
+function emitHighlight(nodes: readonly AdfNode[], depth: number, range: NodeRange, context: InlineContext): Result<Emission> {
-  let text = ''
+  const inner = emitRun(nodes, depth + 1, range.first, context)
+  if (!inner.ok || inner.value.carry !== undefined) return inner
+  const run = { ...range, depth }
+  return success({
+    segments: [{ escaping: 'none', highlight: 'open', nodes: run, text: highlightDelimiter }, ...inner.value.segments, { escaping: 'none', highlight: 'close', nodes: run, text: highlightDelimiter }],
+  })
+}
+
+// Each node its own span: CommonMark reads two adjacent text nodes in one span back as one.
+function emitCodeSpan(nodes: readonly AdfNode[], depth: number, range: NodeRange): Emission {
+  const spans: string[] = []
   for (const node of nodes) {
-    if (node.type !== 'text' || nodeMarks(node).length !== depth + 1) return success({ carry: range })
+    const { text } = node
-    if (typeof node.text !== 'string' || node.text === '') return failure('unsupported-node-shape', 'a text node holds text: this one has none', path)
+    if (!isBareText(node) || nodeMarks(node).length !== depth + 1 || typeof text !== 'string' || text === '' || /[\n\r]/.test(text) || holdsNullCharacter(text)) return { carry: range }
-    if (nodeContent(node).length > 0) return failure('unsupported-node-shape', 'a text node holds no content: this one holds some', path)
+    const fence = '`'.repeat(longestBacktickRun(text) + 1)
-    text += node.text
+    spans.push(`${fence}${needsPadding(text) ? ` ${text} ` : text}${fence}`)
   }
-  if (/[\n\r]/.test(text)) return success({ carry: range })
+  return { segments: [syntax(spans.join(textBreakSpelling))] }
-  if (holdsNullCharacter(text)) return failure('unspellable-character', 'a code span holds a null character CommonMark replaces', path)
-  const fence = '`'.repeat(longestBacktickRun(text) + 1)
-  const padded = needsPadding(text) ? ` ${text} ` : text
-  return success({ segments: [syntax(`${fence}${padded}${fence}`)] })
 }
 
 function needsPadding(text: string): boolean {

src/markdown/emit/line-escaping.ts

@@ -1,13 +1,15 @@
+import type { Flavour } from '../plain/conventions.ts'
 import type { LineContainer } from '../line-container.ts'
 import { backslashEscape, escapesLineClaim, inlineHtmlConstruct, opensBracketedAutolink, opensEmailAutolink, type LinePosition } from '../commonmark/grammar.ts'
 import { backtickRun, closingBacktickRun } from '../commonmark/backtick-runs.ts'
 import { claimsDirectivePrefix } from '../directive-syntax.ts'
 import { delimiterFlags, isWordCharacter, matchEmphasis, runLength } from '../commonmark/emphasis-matching.ts'
+import { highlightDelimiter, highlightFlanking } from '../plain/conventions.ts'
 import { isBareDelimiterRow } from '../pipe-table-syntax.ts'
 import { opensLinkDefinition } from '../commonmark/link-reference-definitions.ts'
 import { readEntityReference } from '../commonmark/entity-references.ts'
 
-export type EmphasisRole = 'close' | 'open'
+export type DelimiterRole = 'close' | 'open'
 
 export type InlineEscaping = 'backslash' | 'bracketed' | 'bracketed-link-target' | 'none'
 
@@ -16,11 +18,12 @@ export type NodeRange = { first: number; last: number }
 export type MarkRun = NodeRange & { depth: number }
 
 export type InlineSegment =
-  | { emphasis: EmphasisRole; escaping: 'none'; nodes: MarkRun; text: string }
+  | { emphasis: DelimiterRole; escaping: 'none'; highlight?: undefined; nodes: MarkRun; text: string }
-  | { emphasis?: undefined; escaping: 'none'; nodes: NodeRange; text: string }
+  | { emphasis?: undefined; escaping: 'none'; highlight: DelimiterRole; nodes: MarkRun; text: string }
-  | { emphasis?: undefined; escaping: InlineEscaping; nodes?: undefined; text: string }
+  | { emphasis?: undefined; escaping: 'none'; highlight?: undefined; nodes: NodeRange; text: string }
+  | { emphasis?: undefined; escaping: InlineEscaping; highlight?: undefined; nodes?: undefined; text: string }
 
-export type AssembledLine = { line: string; openingLinkAsDirective?: true; unspellableRun: MarkRun | undefined }
+export type AssembledLine = { line: string; openingLinkAsDirective?: true; unspellableRuns: MarkRun[] }
 
 type ScanLine = { position: LinePosition; start: number; text: string }
 
@@ -32,8 +35,8 @@ const delimiters = ['*', '_', '`', '~']
 
 const followsLinkText = /[([]/
 
-export function assembleInlineLine(segments: readonly InlineSegment[], container: LineContainer): AssembledLine {
+export function assembleInlineLine(segments: readonly InlineSegment[], container: LineContainer, flavour: Flavour): AssembledLine {
-  return escape(resolveEmphasis(segments), container)
+  return escape(resolveEmphasis(segments), container, flavour === 'plain')
 }
 
 function resolveEmphasis(segments: readonly InlineSegment[]): InlineSegment[] {
@@ -65,11 +68,11 @@ function resolveEmphasis(segments: readonly InlineSegment[]): InlineSegment[] {
   return resolved
 }
 
-function escape(segments: readonly InlineSegment[], container: LineContainer): AssembledLine {
+function escape(segments: readonly InlineSegment[], container: LineContainer, highlights: boolean): AssembledLine {
   const scan = segments.map((segment) => segment.text).join('')
   const escapings: InlineEscaping[] = []
   for (const segment of segments) for (let index = 0; index < segment.text.length; index += 1) escapings.push(segment.escaping)
-  const escaped = escapeClosedRuns(scan, escapings, escapeClaims(scan, escapings, container))
+  const escaped = escapeClosedRuns(scan, escapings, escapeClaims(scan, escapings, container, highlights))
   const placements: number[] = []
   let output = ''
   for (let index = 0; index < scan.length; index += 1) {
@@ -78,34 +81,45 @@ function escape(segments: readonly InlineSegment[], container: LineContainer): A
     output += scan.charAt(index)
   }
   if (container === 'paragraph' && opensLinkDefinition(output)) {
-    if (segments[0]?.nodes !== undefined) return { line: output, openingLinkAsDirective: true, unspellableRun: undefined }
+    if (segments[0]?.nodes !== undefined) return { line: output, openingLinkAsDirective: true, unspellableRuns: [] }
-    return { line: `\\${output}`, unspellableRun: unspellableRun(segments, output, placements) }
+    return { line: `\\${output}`, unspellableRuns: unspellableRuns(segments, output, placements) }
   }
-  return { line: output, unspellableRun: unspellableRun(segments, output, placements) }
+  return { line: output, unspellableRuns: unspellableRuns(segments, output, placements) }
 }
 
-function escapeClaims(scan: string, escapings: readonly InlineEscaping[], container: LineContainer): ReadonlySet<number> {
+function escapeClaims(scan: string, escapings: readonly InlineEscaping[], container: LineContainer, highlights: boolean): ReadonlySet<number> {
   const escaped = new Set<number>()
   const linkClose = lastLinkClose(scan, escapings)
   let line = scanLine(scan, 0)
   let afterEscape = false
+  // Whether the `=` before opens a `==` the reader takes whole, so this one starts nothing.
+  let pairsEquals = false
   for (let index = 0; index < scan.length; index += 1) {
     if (index > line.start + line.text.length) line = scanLine(scan, line.start + line.text.length + 1)
     const escaping = escapings[index]
     const escapable = escaping === 'backslash' || escaping === 'bracketed'
+    const opensEquals: boolean = highlights && !pairsEquals && scan.startsWith(highlightDelimiter, index)
     const claimed: boolean =
       (escapable &&
-        (claimsLineStart(line, index, container) ||
+        ((opensEquals && claimsHighlight(scan, index)) ||
+          claimsLineStart(line, index, container) ||
           mergesWithSyntax(scan, escapings, index) ||
           opensConstruct(scan, linkClose, index, escaping === 'bracketed', container, afterEscape))) ||
       (escaping === 'bracketed-link-target' &&
         ((scan.charAt(index) === '`' && opensCodeSpan(scan, index, afterEscape)) || claimsDirectivePrefix(scan, index)))
     if (claimed) escaped.add(index)
     afterEscape = claimed
+    pairsEquals = opensEquals && !claimed
   }
   return escaped
 }
 
+// Like an emphasis run, a `==` in text escapes where the reader can open or close with it.
+function claimsHighlight(scan: string, index: number): boolean {
+  const flanking = highlightFlanking(scan, index)
+  return flanking.opens || flanking.closes
+}
+
 // CommonMark reads no escape inside a code span, so a backtick string an escape forms or splits off still closes one an earlier bare run opens.
 function escapeClosedRuns(scan: string, escapings: readonly InlineEscaping[], claimed: ReadonlySet<number>): ReadonlySet<number> {
   const escaped = new Set(claimed)
@@ -134,10 +148,27 @@ function escapeClosedRuns(scan: string, escapings: readonly InlineEscaping[], cl
   return escaped
 }
 
-function unspellableRun(segments: readonly InlineSegment[], output: string, placements: readonly number[]): MarkRun | undefined {
+// One emphasis run, the innermost, or every highlight run the line cannot spell.
+function unspellableRuns(segments: readonly InlineSegment[], output: string, placements: readonly number[]): MarkRun[] {
   const { nodes, runs } = emittedRuns(segments, placements, output)
   const pair = misflanked(runs) ?? unpaired(runs)
-  return pair === undefined ? undefined : nodes[pair]
+  const run = pair === undefined ? undefined : nodes[pair]
+  return run === undefined ? unreadHighlights(segments, output, placements) : [run]
+}
+
+// No `==` in text can open or close, and highlights never nest, so a pair reads back where each delimiter flanks.
+function unreadHighlights(segments: readonly InlineSegment[], output: string, placements: readonly number[]): MarkRun[] {
+  const unread: MarkRun[] = []
+  let cursor = 0
+  for (const segment of segments) {
+    const start = placements[cursor] ?? 0
+    cursor += segment.text.length
+    if (segment.highlight === undefined) continue
+    const flanking = highlightFlanking(output, start)
+    const flanks = segment.highlight === 'open' ? flanking.opens : flanking.closes
+    if (!flanks && unread.at(-1) !== segment.nodes) unread.push(segment.nodes)
+  }
+  return unread
 }
 
 function misflanked(runs: readonly EmittedRun[]): number | undefined {

src/markdown/emit/pipe-table.ts

@@ -1,10 +1,11 @@
 import type { AdfNode } from '../../adf/document.ts'
 import type { ConvertErrorPath } from '../../result.ts'
-import { carriesOnly, nodeContent } from '../../adf/document.ts'
+import type { Flavour } from '../plain/conventions.ts'
+import { holdsOnlyAttributes, nodeContent } from '../../adf/document.ts'
 import { spellPipeDelimiter, spellPipeRow } from '../pipe-table-syntax.ts'
 import { tryPipeCell } from './inline-line.ts'
 
-export function tryPipeTable(node: AdfNode, path: ConvertErrorPath): string | undefined {
+export function tryPipeTable(node: AdfNode, path: ConvertErrorPath, flavour: Flavour): string | undefined {
   const rows = pipeRows(node)
   if (rows === undefined) return undefined
   const lines: string[] = []
@@ -12,7 +13,7 @@ export function tryPipeTable(node: AdfNode, path: ConvertErrorPath): string | un
     const cells: string[] = []
     for (const [cellIndex, paragraph] of row.entries()) {
       const content = nodeContent(paragraph)
-      const line = content.length === 0 ? '' : tryPipeCell(content, [...path, 'content', rowIndex, 'content', cellIndex, 'content', 0])
+      const line = content.length === 0 ? '' : tryPipeCell(content, [...path, 'content', rowIndex, 'content', cellIndex, 'content', 0], flavour)
       if (line === undefined) return undefined
       cells.push(line)
     }
@@ -25,16 +26,16 @@ export function tryPipeTable(node: AdfNode, path: ConvertErrorPath): string | un
 function pipeRows(node: AdfNode): AdfNode[][] | undefined {
   const rows = nodeContent(node)
   const columns = rows[0] === undefined ? 0 : nodeContent(rows[0]).length
-  if (!carriesOnly(node, []) || columns === 0) return undefined
+  if (!holdsOnlyAttributes(node, []) || columns === 0) return undefined
   const grid: AdfNode[][] = []
   for (const [index, row] of rows.entries()) {
     const cells = nodeContent(row)
-    if (row.type !== 'tableRow' || !carriesOnly(row, []) || cells.length !== columns) return undefined
+    if (row.type !== 'tableRow' || !holdsOnlyAttributes(row, []) || cells.length !== columns) return undefined
     const wanted = index === 0 ? 'tableHeader' : 'tableCell'
     const paragraphs: AdfNode[] = []
     for (const cell of cells) {
       const paragraph = plainParagraph(cell)
-      if (paragraph === undefined || cell.type !== wanted || !carriesOnly(cell, [])) return undefined
+      if (paragraph === undefined || cell.type !== wanted || !holdsOnlyAttributes(cell, [])) return undefined
       paragraphs.push(paragraph)
     }
     grid.push(paragraphs)
@@ -45,6 +46,6 @@ function pipeRows(node: AdfNode): AdfNode[][] | undefined {
 function plainParagraph(cell: AdfNode): AdfNode | undefined {
   const content = nodeContent(cell)
   const paragraph = content[0]
-  if (paragraph === undefined || content.length !== 1 || paragraph.type !== 'paragraph' || !carriesOnly(paragraph, [])) return undefined
+  if (paragraph === undefined || content.length !== 1 || paragraph.type !== 'paragraph' || !holdsOnlyAttributes(paragraph, [])) return undefined
   return paragraph
 }

src/markdown/empty-keys.ts

@@ -0,0 +1,32 @@
+import type { DirectiveAttributes, DirectiveValue, Read } from './directive-syntax.ts'
+import type { EmptyKey } from '../adf/document.ts'
+import { emptyKeys } from '../adf/document.ts'
+import { unsupportedNodeShape } from './directive-syntax.ts'
+
+type EmptyKeysRead = { empty: ReadonlySet<EmptyKey>; rest: Map<string, DirectiveValue> }
+
+const emptyValue = 'empty'
+
+// spec/flavour.md, Attributes: no attribute value spells an empty object or array.
+export function spellEmptyKeys(held: Parameters<typeof emptyKeys>[0]): [string, string][] {
+  return emptyKeys(held).map((key) => [key, emptyValue])
+}
+
+export function spellsEmpty(value: DirectiveValue | undefined): boolean {
+  return value?.spelling === emptyValue
+}
+
+// `held` is whether the directive spells an attribute outside {attrs}: an argument or a content slot.
+export function readEmptyKeys(type: string, attributes: DirectiveAttributes, keys: readonly EmptyKey[], held: boolean): Read<EmptyKeysRead> {
+  const rest = new Map(attributes)
+  const empty = new Set<EmptyKey>()
+  for (const key of keys) {
+    const spelled = rest.get(key)
+    if (spelled === undefined) continue
+    if (!spellsEmpty(spelled)) return { fault: unsupportedNodeShape(`the reserved key ${key} takes only the value ${emptyValue}: this one spells ${key}=${spelled.spelling}`) }
+    empty.add(key)
+    rest.delete(key)
+  }
+  if (empty.has('attrs') && (held || [...rest.keys()].some((key) => key !== 'marks'))) return { fault: unsupportedNodeShape(`${type} spells attrs=empty beside another attribute, an argument or a [content] slot: drop attrs=empty, or the rest`) }
+  return { value: { empty, rest } }
+}

src/markdown/mark-spellings.ts

@@ -7,6 +7,7 @@ import { holdsEntityReference } from './commonmark/entity-references.ts'
 import { isAutolink } from './commonmark/grammar.ts'
 import { isMarkType, markAttributes } from '../adf/mark-attributes.ts'
 import { nodeAttrs, nodeMarks } from '../adf/document.ts'
+import { spellEmptyKeys } from './empty-keys.ts'
 import { vocabularyPairs } from '../adf/attribute-vocabulary.ts'
 
 type Spelling = { kind: 'code' | 'directive' | 'link'; spelling?: undefined } | { kind: 'emphasis'; spelling: string }
@@ -55,7 +56,10 @@ function isBareLink(nodes: readonly AdfNode[], href: string, marksInside: number
   return nodes.length === 1 && node !== undefined && node.type === 'text' && node.text === href && nodeMarks(node).length === marksInside
 }
 
-export function spellMarkAttributes(mark: AdfMark, vocabulary: AttributeVocabulary): string | undefined {
+// `undefined` where the spelling holds no such attrs: only a directive spells attrs=empty.
-  const pairs = vocabularyPairs(nodeAttrs(mark), vocabulary, [])
+export function spellMarkAttributes(mark: AdfMark, spelling: MarkSpelling): string | undefined {
-  return pairs === undefined ? undefined : spellAttributes(spellVocabulary(pairs))
+  const pairs = vocabularyPairs(nodeAttrs(mark), spelling.attributes, [])
+  const empty = spellEmptyKeys(mark)
+  if (pairs === undefined || (empty.length > 0 && spelling.kind !== 'directive')) return undefined
+  return spellAttributes([...spellVocabulary(pairs), ...empty])
 }

src/markdown/opaque-carry.ts

@@ -1,32 +1,49 @@
 import type { AdfNode } from '../adf/document.ts'
 import type { DirectiveSpan, Read } from './directive-syntax.ts'
 import type { JsonSpelling } from '../canonical-json.ts'
+import type { JsonValue } from '../json-value.ts'
 import { failure, success, type ConvertErrorPath, type Result } from '../result.ts'
 import { fencedCodeBlock } from './commonmark/backtick-runs.ts'
+import { infoStringCarries } from './commonmark/grammar.ts'
 import { isAdfNode } from '../adf/document.ts'
 import { isJsonValue, nestingDepth, overNested } from '../json-value.ts'
 import { largestNesting } from '../nesting.ts'
-import { malformedDirective, readSoleStringAttribute, spellAttributes, spellInlineLeafDirective, spellStringAttribute, unsupportedNodeShape } from './directive-syntax.ts'
+import { directiveEscape, malformedDirective, readSoleStringAttribute, spellAttributes, spellDirectiveOpener, spellInlineLeafDirective, spellStringAttribute, unsupportedNodeShape } from './directive-syntax.ts'
 import { serializeCanonicalJson } from '../canonical-json.ts'
 
+export const carryFencePrefix = 'adf:'
+
 export const carryName = 'carry'
 
 const jsonAttribute = 'json'
 
+// spec/flavour.md, The opaque carry: the info string names the type wherever it carries the type back.
 export function carriedBlock(node: AdfNode, path: ConvertErrorPath, depth: number): Result<{ headroom: number; text: string }> {
-  const json = carriedJson(node, 'two-space', path, largestNesting - depth)
+  const { type, ...untyped } = node
+  const named = infoStringCarries(type)
+  const json = carriedJson(node, named ? untyped : node, 'two-space', path, largestNesting - depth)
   if (!json.ok) return json
-  return success({ headroom: json.value.headroom, text: fencedCodeBlock(carryName, json.value.json) })
+  return success({ headroom: json.value.headroom, text: fencedCodeBlock(`${carryFencePrefix}${named ? type : ''}`, json.value.json) })
 }
 
 export function carriedInline(node: AdfNode, path: ConvertErrorPath): Result<string> {
-  const json = carriedJson(node, 'compact', path, largestNesting)
+  const json = carriedJson(node, node, 'compact', path, largestNesting)
   if (!json.ok) return json
   return success(spellInlineLeafDirective(carryName, spellAttributes([[jsonAttribute, spellStringAttribute(json.value.json)]])))
 }
 
-export function readCarriedBlock(body: string, depth: number): Read<AdfNode> {
+// The type a fence's info string names, `undefined` where the info string opens no carry.
-  return readCarriedJson(body, 'two-space', largestNesting - depth)
+export function carryFenceType(info: string): string | undefined {
+  return info.startsWith(carryFencePrefix) ? info.slice(carryFencePrefix.length) : undefined
+}
+
+export function readCarriedBlock(type: string, body: string, depth: number): Read<AdfNode> {
+  if (type !== '' && !infoStringCarries(type)) {
+    return { fault: unsupportedNodeShape(`the carry fence names a type no info string carries back: spell it ${carryFencePrefix} with the type in the JSON; ${fenceEscape(type)}`) }
+  }
+  const read = readCarriedJson(body, 'two-space', largestNesting - depth, type)
+  if (read.fault !== undefined || type !== '' || !infoStringCarries(read.value.type)) return read
+  return { fault: unsupportedNodeShape(`the ${carryFencePrefix} fence holds a type its info string can carry: spell the fence ${carryFencePrefix}${read.value.type} and drop type from the JSON`) }
 }
 
 export function readCarriedInline(span: DirectiveSpan): Read<AdfNode> | undefined {
@@ -36,28 +53,44 @@ export function readCarriedInline(span: DirectiveSpan): Read<AdfNode> | undefine
   return readCarriedJson(spelled.value, 'compact', largestNesting)
 }
 
-function carriedJson(node: AdfNode, spelling: JsonSpelling, path: ConvertErrorPath, levels: number): Result<{ headroom: number; json: string }> {
+function carriedJson(node: AdfNode, spelled: object, spelling: JsonSpelling, path: ConvertErrorPath, levels: number): Result<{ headroom: number; json: string }> {
   const headroom = levels - nestingDepth(node)
-  if (!isJsonValue(node) || headroom < 0) {
+  if (!isJsonValue(spelled) || headroom < 0) {
     return failure('unsupported-nesting-depth', `a carried node's JSON nests deeper than the ${levels} levels its position leaves`, path)
   }
-  return success({ headroom, json: serializeCanonicalJson(node, spelling) })
+  return success({ headroom, json: serializeCanonicalJson(spelled, spelling) })
 }
 
-function readCarriedJson(raw: string, spelling: JsonSpelling, levels: number): Read<AdfNode> {
+// `type` is the one the fence's info string names, `undefined` for the inline carry.
+function readCarriedJson(raw: string, spelling: JsonSpelling, levels: number, type?: string): Read<AdfNode> {
+  const wayOut = type === undefined ? directiveEscape : fenceEscape(type)
   const parsed = parseJsonText(raw)
-  if (parsed === undefined) return { fault: malformedDirective('the opaque carry holds invalid JSON') }
+  if (parsed === undefined) return { fault: malformedDirective(`the opaque carry holds invalid JSON; ${wayOut}`) }
   const { value } = parsed
   if (!isJsonValue(value)) return { fault: unsupportedNodeShape('the opaque carry holds a number JSON cannot spell') }
-  if (overNested(value, levels)) {
+  const typed = type === undefined || type === '' ? { value } : typedValue(value, type)
+  if (typed.fault !== undefined) return typed
+  const held = typed.value
+  if (overNested(held, levels)) {
     return { fault: { code: 'unsupported-nesting-depth', message: `a carried node's JSON nests deeper than the ${levels} levels its position leaves` } }
   }
   if (serializeCanonicalJson(value, spelling) !== raw) {
     const shape = spelling === 'compact' ? 'compact, keys sorted' : 'two-space indent, keys sorted'
-    return { fault: unsupportedNodeShape(`the opaque carry spells its node's JSON canonically: ${shape}`) }
+    return { fault: unsupportedNodeShape(`the opaque carry spells its node's JSON canonically: ${shape}; ${wayOut}`) }
   }
-  if (!isAdfNode(value)) return { fault: unsupportedNodeShape("the opaque carry holds one ADF node's JSON: this JSON is no ADF node") }
+  if (!isAdfNode(held)) return { fault: unsupportedNodeShape(`the opaque carry holds one ADF node's JSON: this JSON is no ADF node; ${wayOut}`) }
-  return { value }
+  return { value: held }
+}
+
+// A code fence the carry claims stays code under the directive, whose language rides the attribute.
+function fenceEscape(type: string): string {
+  return `${spellDirectiveOpener('codeBlock', undefined, spellAttributes([['language', spellStringAttribute(`${carryFencePrefix}${type}`)]]))} around a bare fence keeps it a code block`
+}
+
+function typedValue(value: JsonValue, type: string): Read<JsonValue> {
+  if (value === null || typeof value !== 'object' || Array.isArray(value)) return { value }
+  if ('type' in value) return { fault: unsupportedNodeShape(`the ${carryFencePrefix}${type} fence names its node's type: this JSON holds a type as well; ${fenceEscape(type)}`) }
+  return { value: { ...value, type } }
 }
 
 function parseJsonText(raw: string): { value: unknown } | undefined {

src/markdown/parse/directive-marks.ts

@@ -3,8 +3,9 @@ import type { ConvertFault } from '../../result.ts'
 import type { DirectiveAttributes } from '../directive-syntax.ts'
 import type { MarkSpelling } from '../mark-spellings.ts'
 import { directivePrefix } from '../directive-syntax.ts'
-import { failure, success, type ConvertErrorPath, type Result } from '../../result.ts'
+import { failure, faulted, success, type ConvertErrorPath, type Result } from '../../result.ts'
 import { markSpelling } from '../mark-spellings.ts'
+import { readEmptyKeys } from '../empty-keys.ts'
 import { readVocabulary } from './directive-attributes.ts'
 
 export function readDirectiveMark(name: string, attributes: DirectiveAttributes, path: ConvertErrorPath): Result<AdfMark> | undefined {
@@ -12,8 +13,11 @@ export function readDirectiveMark(name: string, attributes: DirectiveAttributes,
   if (spelling === undefined) return undefined
   const markdown = markdownForm(spelling)
   if (markdown !== undefined) return failure('unsupported-node-shape', `${name} is spelled ${markdown}, never as a directive`, path)
-  const attrs = readVocabulary(name, attributes, spelling.attributes, undefined, path)
+  const empty = readEmptyKeys(name, attributes, ['attrs'], false)
+  if (empty.fault !== undefined) return faulted(empty.fault, path)
+  const attrs = readVocabulary(name, empty.value.rest, spelling.attributes, undefined, path)
   if (!attrs.ok) return attrs
+  if (empty.value.empty.has('attrs')) return success({ attrs: {}, type: name })
   return success(Object.keys(attrs.value).length === 0 ? { type: name } : { attrs: attrs.value, type: name })
 }