Answer product-owner round 1: list each input the new code takes in MIGRATION's table, a String object among them, and give htmlToAdf the code

CHANGELOG.md

@@ -3,9 +3,10 @@
 ## Unreleased
 
 - **Breaking:** `markdownToAdf` and `plainMarkdownToAdf` refuse a value that is not a string with
-  the new code `not-a-string`, at position `{ line: 1, offset: 0 }`. Before, `null` and `undefined`
-  threw a `TypeError` and a number read as an empty document. A `switch` over `ConvertErrorCode`
-  naming every code needs the new case.
+  the new code `not-a-string`, at position `{ line: 1, offset: 0 }`. Before, `null`, `undefined`
+  and a non-empty array threw a `TypeError`, a `String` object converted its text, and a number
+  read as an empty document; pass `String(value)` where a boxed string arrives. A `switch` over
+  `ConvertErrorCode` naming every code needs the new case.
 - **Breaking:** an attribute value that is not a plain object, array or JSON primitive, such as a
   `Date`, `Map`, typed array or class instance, makes `isAdfDocument` return `false` and the
   converters refuse it as `not-an-adf-document`. Before, the converters wrote it as `{}` or its own

MIGRATION.md

@@ -81,7 +81,8 @@ converts; markdown the parser refused with one of them now refuses with the code
 | 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` |
 | an empty node the `::taskItem` spelling row names, written with a closer | `unsupported-node-shape` | parses |
+| `null`, `undefined` or a non-empty array, on parse | throws a `TypeError` | `not-a-string` |
+| a `String` object, on parse | the document its text spells | `not-a-string`; pass `String(value)` |
+| a number, a boolean, a plain object or an empty array, on parse | an empty document | `not-a-string` |
 
-`ConvertErrorCode` gains `not-a-string`: a `switch` naming every code needs its case. The markdown
-readers return it for a value that is not a string, which threw or read as an empty document
-before.
+`ConvertErrorCode` gains `not-a-string`: a `switch` naming every code needs its case.

README.md

@@ -187,7 +187,7 @@ Parsing — `markdownToAdf` and `plainMarkdownToAdf`, and `htmlToAdf` at `0.2.0`
 | --- | --- | --- |
 | `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 |
-| `not-a-string` | the value handed in is not a string: `null`, `undefined`, a number, an object | pass the markdown as a string; the message names the type passed |
+| `not-a-string` | the value handed in is not a string: `null`, `undefined`, a number, an object, a `String` object among them | pass the input as a string, `String(value)` for a `String` object; the message names the type passed |
 | `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 |

docs/decisions.md

@@ -383,9 +383,9 @@ handles one cause alike whichever node, attribute or direction raised it.
   knows which direction it called and parting them after `0.1.0` is MAJOR (2026-09-23).
 - A non-finite number takes two codes: `unsupported-node-shape` parsing, `not-an-adf-document`
   emitting — no document holds one, so no round-trip crosses them (2026-09-23).
-- A value handed to a markdown reader that is not a string is `not-a-string`, its position
-  `{ line: 1, offset: 0 }` and its path empty: no code read true of it, and `not-an-adf-document`
-  names the other direction's input (2026-10-05).
+- A value handed to a reader of markdown or HTML that is not a string is `not-a-string`, its
+  position `{ line: 1, offset: 0 }` and its path empty: no code read true of it, and
+  `not-an-adf-document` names the other direction's input (2026-10-05).
 
 ## `message` and `path`
 

todo.md

@@ -67,7 +67,8 @@
 ### 7. Ship HTML: `adfToHtml`, `htmlToAdf`, and `markdownToHtml` / `htmlToMarkdown` composed through ADF.
 
 Lands after items 6, 59, 60, 61 and 62. The CommonMark spec suite also runs against
-`markdownToHtml`. The README documents HTML as it documents markdown.
+`markdownToHtml`. The README documents HTML as it documents markdown. `htmlToAdf` refuses a value
+that is not a string as `not-a-string` (`docs/decisions.md` §Which code a cause takes).
 
 ### 45. Replace `isAdfDocument` with a reader returning `Result<AdfDocument>`.