Answer architecture round 2: 0 🔴, 1 🟡; the ClaimedPrefix comment sits on its type again, README names the marks fallback

README.md

@@ -317,8 +317,9 @@ Ping !adf:mention[@Mikael]{id=5b10a2} — !adf:status[In review]{color=yellow}
 - Attributes are `{key=value key2="two words"}`: keys alphabetical, a value bare where it is
   `[A-Za-z0-9_-]+`, else double-quoted with JSON string escaping. A number or JSON value is spelled as
   canonical JSON, but `colwidth` is its widths joined by commas, `colwidth="340,420"`, and a block's
-  `marks` names each mark with its attributes, `marks="breakout{mode=wide}"`. An empty `attrs`, `content` or `marks` key is spelled `{attrs=empty}`,
-  `{content=empty}` or `{marks=empty}`.
+  `marks` names each mark with its attributes, `marks="breakout{mode=wide}"`, keeping the JSON array
+  where a mark's type or attributes are ones the flavour does not list. An empty `attrs`, `content`
+  or `marks` key is spelled `{attrs=empty}`, `{content=empty}` or `{marks=empty}`.
 - Three reserved names build no node: `!adf:carry` is the inline opaque carry, `!adf:doc {content=none}`
   spells a document holding no `content` key, and `!adf:textBreak{}` parts two adjacent text nodes
   CommonMark would read back as one.

src/markdown/directive-syntax.ts

@@ -11,9 +11,9 @@ import { serializeCanonicalJson } from '../canonical-json.ts'
 
 export type AttributeReading = { refusal: 'kind' | 'nesting'; value?: undefined } | { refusal?: undefined; value: VocabularyValue }
 
-// Proof that `!adf:` stands at `index`; only `claimDirectivePrefix` builds one.
 export type Attributes = { attributes: DirectiveAttributes; end: number }
 
+// Proof that `!adf:` stands at `index`; only `claimDirectivePrefix` builds one.
 export type ClaimedPrefix = { readonly [claimedPrefix]: true; readonly index: number }
 
 export type DirectiveValue = { decoded: string; spelling: string }