10c - adfToPlainMarkdown and plainMarkdownToAdf exported, whitespace-only leaves trimmed at a line end

README.md

@@ -86,6 +86,9 @@ adfToMarkdown(doc: AdfDocument): Result<string>
 markdownToAdf(markdown: string): Result<AdfDocument, ParseError>
 isAdfDocument(v: unknown): v is AdfDocument
 
+adfToPlainMarkdown(doc: AdfDocument): Result<string>
+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
@@ -94,6 +97,42 @@ htmlToMarkdown(html: string): Result<string>              // 0.2.0, via ADF
 
 `Result<T>` is `{ ok: true; value: T } | { ok: false; error: ConvertError }` — nothing throws.
 
+## Plain markdown
+
+`adfToPlainMarkdown` writes markdown other tools render — GitHub, GitLab, Obsidian and the like —
+keeping the content and dropping the rest: attributes, colours, layout, identity. It refuses only
+`not-an-adf-document`, `unsupported-document-version` and `unsupported-nesting-depth`, and writes
+no directive. `plainMarkdownToAdf` reads through `markdownToAdf`, refusing what it refuses, and
+lifts the conventions below back into nodes, reading other tools' spellings too. Markdown
+`adfToPlainMarkdown` wrote reads back and writes again byte for byte; the document it came from
+does not come back.
+
+| 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 |
+| `expand`, `nestedExpand` | Obsidian's folded callout, `> [!NOTE]- Title` | `-` or `+` after any word; 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 |
+| `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 | — |
+| 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:
+  `_(image not included)_`, `_(jira-issues-table not included)_`, `_(synced block not included)_`,
+  `_(link card not included)_`, `_(extension not included)_`.
+- `code`, `em`, `link`, `strike` and `strong` stay; every other mark drops, keeping its text, and
+  so does a mark CommonMark cannot spell where it stands.
+- A newline in text is a hard break, edge whitespace is trimmed, carriage returns and null
+  characters are removed, and an empty paragraph drops.
+- 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`.
+
 ## The errors
 
 An ADF node type this version does not know is not an error: it is carried opaquely and restores