cjk - a letter of a script written without spaces bounds a highlight

README.md

@@ -133,7 +133,7 @@ read replaces mentions, attachments and macros with text.
 | `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` |
 | `taskList` | `- [x] Done`, `- [ ] Todo` | a bullet list whose every item is so marked, `[X]` too |
-| `backgroundColor` | `==text==` | `==text==` on one line, the text touching both delimiters, bounded outside by whitespace, punctuation or a line edge, in the editor's default highlight `#f8e6a0` |
+| `backgroundColor` | `==text==` | `==text==` on one line, the text touching both delimiters, bounded outside by whitespace, punctuation, a line edge or a letter of a script written without spaces (Han, Hiragana, Katakana, Thai, Lao, Khmer, Myanmar), 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 | — |

docs/decisions.md

@@ -145,14 +145,16 @@ parentheses: `> [!faq]- See [x](http://y)` reads to the title `See x (http://y)`
 
 ## 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. Goal 5. 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 letter of a script written without spaces bounding them, so `は==日本語==で`
-list item dropping (3 of 3), and a list's numbering overflowing into bullets (3 of 3, 5 of 7).
+highlights (3 of 3), the external image's two forms (6 of 7), the omission notes and a rule
+opening a list item dropping (3 of 3), and a list's numbering overflowing into bullets (3 of 3,
+5 of 7).
 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,

src/markdown/emit/plain-reduction.test.ts

@@ -148,6 +148,8 @@ test('spells a highlight as a == pair around the run, whatever its colour', () =
   assert.equal(plain(paragraph(text('a', highlight('#fff'), code), text('b', highlight('#fff')))), '`a`==b==\n')
   assert.equal(plain(paragraph(text('=', highlight('#fff')), text(' '), text('a==b', highlight('#fff')))), '==\\=== ==a==b==\n')
   assert.equal(plain(paragraph(text('x'), text('y', highlight('#fff')), text(' z'))), 'xy z\n')
+  assert.equal(plain(paragraph(text('この機能は'), text('日本語', highlight('#fff')), text('でのみ'))), 'この機能は==日本語==でのみ\n')
+  assert.equal(plain(paragraph(text('日==本==語'))), '日\\==本\\==語\n')
 })
 
 test('escapes text a renderer would take as a flavour marker, and only there', () => {

src/markdown/parse/plain-markdown-to-adf.test.ts

@@ -149,6 +149,9 @@ test('reads a == pair to the editor default highlight, Yellow200 #f8e6a0 in @atl
   assert.deepEqual(read('==`a`==\n'), [paragraph(text('a', code))])
   assert.deepEqual(read('x==y==z ==a == b==, (==c==) _d_==e==\n'), [paragraph(text('x==y==z '), text('a == b', highlight), text(', ('), text('c', highlight), text(') '), text('d', em), text('e', highlight))])
   assert.deepEqual(read('😀==b== ==c==😀 é==d==\n'), [paragraph(text('😀'), text('b', highlight), text(' '), text('c', highlight), text('😀 é==d=='))])
+  assert.deepEqual(read('この機能は==日本語==でのみ、中文==重点==内容、ภาษา==ไทย==ดี a==日本==b\n'), [
+    paragraph(text('この機能は'), text('日本語', highlight), text('でのみ、中文'), text('重点', highlight), text('内容、ภาษา'), text('ไทย', highlight), text('ดี a==日本==b')),
+  ])
   assert.deepEqual(read('# ==h==\n\n| ==c== |\n| --- |\n'), [
     node('heading', { level: 1 }, text('h', highlight)),
     bare('table', bare('tableRow', bare('tableHeader', paragraph(text('c', highlight))))),
@@ -196,7 +199,7 @@ test('reads what the reduction wrote back to the node it reduced, less the attri
 test('reads text the writer kept from reading as a marker back as text', () => {
   const quote = bare('blockquote', said('[!NOTE] x'))
   const list = bare('bulletList', bare('listItem', said('[x] a')), bare('listItem', said('[ ] b')))
-  assert.deepEqual(roundTripped(said('==x== a==b'), quote, list), [said('==x== a==b'), quote, list])
+  assert.deepEqual(roundTripped(said('==x== a==b 日==本==語'), quote, list), [said('==x== a==b 日==本==語'), quote, list])
   assert.deepEqual(roundTripped(bare('taskList', task('DONE', text('[x] ==a==')))), [bare('taskList', task('DONE', text('[x] ==a==')))])
 })
 

src/markdown/plain-conventions.ts

@@ -34,6 +34,8 @@ const panelTypesByWord: Readonly<Record<string, string>> = {
   warning: 'warning',
 }
 
+const unspacedScript = /^[\p{Script=Han}\p{Script=Hiragana}\p{Script=Katakana}\p{Script=Khmer}\p{Script=Lao}\p{Script=Myanmar}\p{Script=Thai}]$/u
+
 export function alertMarker(panelType: unknown): string {
   const word = typeof panelType === 'string' && Object.hasOwn(alertWords, panelType) ? alertWords[panelType] : undefined
   return `[!${word ?? 'NOTE'}]`
@@ -60,7 +62,11 @@ export function highlightFlanking(source: string, index: number): { closes: bool
   const end = index + highlightDelimiter.length
   const before = Array.from(source.slice(Math.max(0, index - 2), index)).at(-1) ?? ''
   const after = Array.from(source.slice(end, end + 2))[0] ?? ''
-  return { closes: flanks(before) && !isWordCharacter(after), opens: flanks(after) && !isWordCharacter(before) }
+  return { closes: flanks(before) && bounds(after), opens: flanks(after) && bounds(before) }
+}
+
+function bounds(character: string): boolean {
+  return !isWordCharacter(character) || unspacedScript.test(character)
 }
 
 function flanks(character: string): boolean {