fix(markdown): support word-internal apostrophes in tags (#6135)

docs/adr/0001-tag-syntax-and-recognition.md

@@ -45,6 +45,7 @@ changing metadata or a separate tag record. Renaming `#Work` to `#work` across 1
 ## Decision drivers
 
 - Work naturally for multilingual personal notes, including numeric tags and emoji.
+- Preserve common word-internal apostrophes without absorbing surrounding quotation punctuation into tag values.
 - Recognize `hello#tag` intentionally without mistaking URL fragments for tags.
 - Give the backend, renderer, editor decoration, and completion the same values and source spans.
 - Use Markdown syntax rather than ad hoc URL or code regular expressions.
@@ -100,6 +101,11 @@ changing metadata or a separate tag record. Renaming `#Work` to `#work` across 1
 **Tag segment**
 : A non-empty component of a hierarchical tag identifier. Slashes separate segments and are not part of any segment.
 
+**Apostrophe joiner**
+: U+0027 APOSTROPHE (`'`) or U+2019 RIGHT SINGLE QUOTATION MARK (`’`) emitted inside a tag segment only when, after emoji-first tokenization, the
+  immediately preceding source code point emits as an `XID_Continue` code point and the immediately following source code point emits as a non-combining
+  `XID_Continue` code point.
+
 **Display value**
 : The direct or implied value presented as a derived tag label. It preserves emitted code points exactly but does not contain ignored default-ignorable code
   points or ignored leading combining marks.
@@ -143,7 +149,7 @@ Introducer          := U+0023 NUMBER SIGN ("#") outside a FullyQualifiedEmoji
 TagSourceSpelling   := TagSegmentSpelling ("/" TagSegmentSpelling)*
 TagSegmentSpelling  := IgnoredPrefix* SegmentStarter SegmentContinuation*
 IgnoredPrefix       := IgnoredDefaultIgnorable | IgnoredLeadingCombiningMark
-SegmentContinuation := ValueUnit | IgnoredDefaultIgnorable
+SegmentContinuation := ValueUnit | ApostropheJoiner | IgnoredDefaultIgnorable
 
 SegmentStarter := EmittedXIDContinueCodePointExceptCombiningMark
                 | FullyQualifiedEmoji
@@ -157,6 +163,9 @@ ValueUnit := EmittedXIDContinueCodePoint
            | "+"
            | "&"
 
+ApostropheJoiner := U+0027 APOSTROPHE ("'")
+                  | U+2019 RIGHT SINGLE QUOTATION MARK ("’")
+
 IgnoredDefaultIgnorable := Default_Ignorable_Code_Point outside a FullyQualifiedEmoji
 IgnoredLeadingCombiningMark := XID_Continue with General_Category Mn or Mc,
                                minus Default_Ignorable_Code_Point, before SegmentStarter
@@ -164,13 +173,14 @@ IgnoredLeadingCombiningMark := XID_Continue with General_Category Mn or Mc,
 
 The grammar recognizes source spelling and emits a tag identifier as follows:
 
-- Each `SegmentStarter` and `ValueUnit` emits its exact source code-point sequence. A `FullyQualifiedEmoji` therefore emits its complete matched sequence.
+- Each `SegmentStarter`, `ValueUnit`, and contextually valid `ApostropheJoiner` emits its exact source code-point sequence. A `FullyQualifiedEmoji`
+  therefore emits its complete matched sequence.
 - Each consumed `/` emits one U+002F SOLIDUS into the identifier.
 - `Introducer`, `IgnoredDefaultIgnorable`, and `IgnoredLeadingCombiningMark` emit nothing.
 
 At every source position, the token priority is the longest `FullyQualifiedEmoji`, then `IgnoredDefaultIgnorable`, then `IgnoredLeadingCombiningMark`, then
-an emitted code point or Memos extension unit. This preserves default-ignorable code points inside matched fully-qualified emoji sequences while omitting
+a contextually valid `ApostropheJoiner`, then an emitted code point or Memos extension unit. This preserves default-ignorable code points inside matched
-them everywhere else.
+fully-qualified emoji sequences while omitting them everywhere else.
 
 The emitted tag identifier is the direct tag value.
 
@@ -199,12 +209,20 @@ Rules:
 12. A non-default-ignorable `XID_Continue` code point whose General Category is `Mn` (Nonspacing Mark) or `Mc` (Spacing Combining Mark) is consumed but
     omitted while it precedes the starter of its segment. The same non-default-ignorable code point is preserved as a value unit after that segment's
     starter.
-13. There is no tag-specific identifier length limit. The enclosing memo-size limit provides the resource bound.
+13. After applying the longest-`FullyQualifiedEmoji` token priority, U+0027 APOSTROPHE and U+2019 RIGHT SINGLE QUOTATION MARK are emitted as
+    `ApostropheJoiner` only when the immediately preceding source code point in the same segment was emitted as an `EmittedXIDContinueCodePoint` and the
+    immediately following source code point can emit as an
+    `EmittedXIDContinueCodePointExceptCombiningMark`. An apostrophe joiner therefore cannot start or end a segment, repeat without an intervening XID
+    code point, adjoin a fully-qualified emoji or Memos extension unit, or join across an ignored code point.
+14. U+02BC MODIFIER LETTER APOSTROPHE (`ʼ`) is already an `XID_Continue` code point. It follows the ordinary XID rules rather than the contextual
+    apostrophe-joiner rule.
+15. There is no tag-specific identifier length limit. The enclosing memo-size limit provides the resource bound.
 
 The grammar is intentionally broader than a programming-language identifier grammar. It does not require the first emitted unit to be `XID_Start`:
 digits, `_`, `-`, `+`, `&`, and fully-qualified emoji can start a segment. Default-ignorable code points and non-default-ignorable `Mn` or `Mc` code points
 may occur before each segment's starter but are omitted from the value. After the starter, those non-default-ignorable `Mn` and `Mc` code points are
-preserved. A slash cannot begin a segment, and segments made only from `-`, `+`, and `&` are explicitly valid.
+preserved. ASCII and right-curly apostrophes are emitted only as contextual joiners between XID code points. A slash cannot begin a segment, and segments
+made only from `-`, `+`, and `&` are explicitly valid.
 
 ### Maximal-prefix scanning
 
@@ -215,12 +233,15 @@ After finding an introducer, the lexer consumes the longest valid `TagSourceSpel
 2. Emit a segment starter, trying the longest matching `FullyQualifiedEmoji` before any shorter unit.
 3. After the starter, preserve non-default-ignorable `XID_Continue` combining marks as ordinary value units; continue consuming default-ignorable code
    points without emitting them.
-4. Consume `/` only when the following source, after any ignored prefix, can emit a segment starter; then consume that segment.
+4. Emit U+0027 or U+2019 as an apostrophe joiner only when, after emoji-first tokenization, the immediately preceding source code point emitted an XID
-5. Stop before a `/` that is leading, trailing, or followed only by an ignored prefix and then another `/`, a non-starter, or the end of the literal-source
+   continuation unit and the immediately following source code point can emit a non-combining XID continuation unit. Otherwise stop before the
+   apostrophe.
+5. Consume `/` only when the following source, after any ignored prefix, can emit a segment starter; then consume that segment.
+6. Stop before a `/` that is leading, trailing, or followed only by an ignored prefix and then another `/`, a non-starter, or the end of the literal-source
    run, leaving that slash and the remaining source unconsumed.
-6. Otherwise stop before the first code point that cannot begin a valid continuation unit.
+7. Otherwise stop before the first code point that cannot begin a valid continuation unit.
-7. Keep the valid prefix already consumed; a later invalid character does not invalidate it.
+8. Keep the valid prefix already consumed; a later invalid character does not invalidate it.
-8. Produce no candidate if the first `TagSegmentSpelling` cannot match.
+9. Produce no candidate if the first `TagSegmentSpelling` cannot match.
 
 ### Candidate enumeration
 
@@ -255,6 +276,13 @@ Examples:
 | `#price€` | `price` | `€` |
 | `#C++` | `C++` | empty |
 | `#R&D` | `R&D` | empty |
+| `#tag's` | `tag's` | empty |
+| `#сім'я` | `сім'я` | empty |
+| `#O’Brien` | `O’Brien` | empty |
+| `#café's` | `café's` | empty |
+| `#users'` | `users` | `'` |
+| `#foo'1️⃣` | `foo` | `'1️⃣` |
+| `#'tag` | none | `'tag` |
 | `#-foo` | `-foo` | empty |
 | `#foo-` | `foo-` | empty |
 | `#---` | `---` | empty |
@@ -380,6 +408,8 @@ deduplicating, counting, filtering, navigating, or performing exact metadata loo
 #café       / #café
 #Ａ          / #A
 #straße     / #STRASSE
+#O'Brien    / #O’Brien
+#O’Brien    / #OʼBrien
 ```
 
 Multiple occurrences that emit exactly equal direct tag values in one memo produce one memo-tag membership. A tag metadata rule may deliberately match
@@ -432,6 +462,16 @@ The following examples are normative for the lexical and context decisions alrea
 | `#2026` | `2026` | Numeric-only identifiers are valid |
 | `#C++` | `C++` | Explicit `+` extension |
 | `#R&D` | `R&D` | Explicit `&` extension |
+| `#tag's` | `tag's` | ASCII apostrophe joins two XID code points |
+| `#сім'я` | `сім'я` | ASCII apostrophe preserves a Ukrainian word |
+| `#O’Brien` | `O’Brien` | Right single quotation mark joins two XID code points |
+| `#café's` | `café's` | An emitted combining mark may precede an apostrophe joiner |
+| `#users'` | `users` | A trailing apostrophe is not a joiner |
+| `#foo'1️⃣` | `foo` | Emoji-first tokenization prevents an apostrophe from adjoining the keycap sequence |
+| `#'tag` | none | An apostrophe cannot start a segment |
+| `'#tag'` | `tag` | Surrounding quotation punctuation remains outside the occurrence |
+| `#rock’n’roll` | `rock’n’roll` | Multiple apostrophe joiners are valid when each independently satisfies the context rule |
+| `#OʼBrien` | `OʼBrien` | U+02BC is an ordinary `XID_Continue` code point |
 | `#` followed by 101 `a` code points | all 101 `a` code points | There is no tag-specific length limit |
 | `#-foo` | `-foo` | Visible connector extensions may begin a segment |
 | `#foo-` | `foo-` | Visible connector extensions may end a segment |
@@ -490,7 +530,9 @@ The following examples are normative for the lexical and context decisions alrea
 - Common multilingual tags, numeric tags, hierarchy characters, and emoji remain expressive.
 - Hierarchical ancestors have one consistent meaning across API membership, exact filters, navigation, and counts.
 - `hello#tag` works consistently while actual Markdown links and URLs are excluded structurally.
-- Markdown punctuation and delimiters such as comma, backtick, currency, and mathematical operators stop an identifier predictably.
+- Common word-internal apostrophes support multilingual words and names while surrounding quotation punctuation remains outside tag values.
+- Unsupported Markdown punctuation, delimiters, currency symbols, and operators stop an identifier predictably; apostrophes are the explicitly
+  constrained exception.
 - Exact equality preserves every emitted code-point distinction and avoids locale-dependent identity rules.
 - Ignoring default-ignorable code points outside emoji avoids invisible tag distinctions while preserving matched fully-qualified emoji sequences.
 - Ignoring leading non-default-ignorable `Mn` and `Mc` code points only before each segment's visible starter avoids invisible-leading segments without
@@ -506,6 +548,8 @@ The following examples are normative for the lexical and context decisions alrea
 - Pinning Unicode data requires maintenance when Unicode and Emoji data are updated.
 - Visually indistinguishable or canonically equivalent source spellings whose emitted values differ remain separate tags unless the user edits their memo
   sources to make those values identical.
+- Visually similar apostrophe spellings such as U+0027, U+2019, and U+02BC remain distinct under exact tag identity.
+- English possessive-looking source such as `#tag's` denotes the complete tag value `tag's`, not `tag` followed by prose.
 - Source spellings that differ only by ignored default-ignorable code points intentionally collapse to the same emitted tag value.
 - Source spellings that differ only by ignored leading combining marks intentionally collapse to the same emitted tag value.
 
@@ -554,6 +598,12 @@ tag. The slash and remaining source stay ordinary Markdown.
 Rejected. Requiring `-`, `+`, or `&` to be medial, non-repeating, or accompanied by a letter would add validation rules without resolving a structural
 ambiguity. They remain ordinary segment units; only `/` has structural meaning.
 
+### Treat apostrophes as unrestricted value units
+
+Rejected. Allowing apostrophes as starters, trailing units, or repeatable ordinary units would absorb surrounding quotation punctuation into values such
+as `tag'` and make quoted source such as `'#tag'` ambiguous. The contextual joiner rule supports words and names while leaving punctuation at tag
+boundaries unconsumed.
+
 ### Recognize compatibility number signs
 
 Rejected. U+FE5F SMALL NUMBER SIGN and U+FF03 FULLWIDTH NUMBER SIGN are visually similar to `#` but are not Markdown syntax. Recognizing only ASCII U+0023

internal/markdown/markdown_test.go

@@ -576,6 +576,16 @@ func TestExtractTagsMemosTagV1(t *testing.T) {
 		{name: "number sign keycap continuation", content: "#first#️⃣", expected: []string{"first#️⃣"}},
 		{name: "exact identity", content: "#Work #work", expected: []string{"Work", "work"}},
 		{name: "no normalization", content: "#café #cafe\u0301", expected: []string{"café", "cafe\u0301"}},
+		{
+			name:     "word internal apostrophes",
+			content:  "#tag's #сім'я #O'Brien #O’Brien #OʼBrien #cafe\u0301's",
+			expected: []string{"tag's", "сім'я", "O'Brien", "O’Brien", "OʼBrien", "cafe\u0301's"},
+		},
+		{
+			name:     "apostrophe boundaries",
+			content:  "'#tag' #users' #'missing #rock''roll #O‘Brien #A\u200d'B",
+			expected: []string{"tag", "users", "rock", "O", "A"},
+		},
 		{name: "ignored spellings deduplicate", content: "#AB #A\u200dB #\u0301AB", expected: []string{"AB"}},
 		{name: "hierarchy expansion", content: "#book/fiction/history", expected: []string{"book", "book/fiction", "book/fiction/history"}},
 		{name: "hierarchy exact dedupe", content: "#book/fiction #book", expected: []string{"book", "book/fiction"}},

internal/markdown/parser/tag.go

@@ -60,6 +60,21 @@ func isSegmentContinuation(r rune) bool {
 	return r == '-' || r == '+' || r == '&' || isXIDContinue(r) && !isDefaultIgnorable(r)
 }
 
+func isApostropheJoiner(r rune) bool {
+	return r == '\'' || r == '\u2019'
+}
+
+func startsNonCombiningXIDContinuation(source []byte) bool {
+	if len(source) == 0 || matchFullyQualifiedEmoji(source) > 0 {
+		return false
+	}
+	r, size := utf8.DecodeRune(source)
+	if r == utf8.RuneError && size == 1 {
+		return false
+	}
+	return isXIDContinue(r) && !isCombiningMark(r) && !isDefaultIgnorable(r)
+}
+
 func matchFullyQualifiedEmoji(source []byte) int {
 	limit := min(len(source), maxEmoji17SequenceBytes)
 	match := 0
@@ -82,6 +97,7 @@ func matchFullyQualifiedEmoji(source []byte) int {
 func scanTagSegment(source []byte) (int, []byte, bool) {
 	pos := 0
 	var value []byte
+	previousWasXIDContinuation := false
 
 starter:
 	for pos < len(source) {
@@ -91,6 +107,7 @@ starter:
 		if emojiLength := matchFullyQualifiedEmoji(source[pos:]); emojiLength > 0 {
 			value = append(value, source[pos:pos+emojiLength]...)
 			pos += emojiLength
+			previousWasXIDContinuation = false
 			break
 		}
 		r, size := utf8.DecodeRune(source[pos:])
@@ -105,6 +122,7 @@ starter:
 		case isSegmentStarter(r):
 			value = append(value, source[pos:pos+size]...)
 			pos += size
+			previousWasXIDContinuation = isXIDContinue(r) && !isDefaultIgnorable(r)
 			break starter
 		default:
 			return 0, nil, false
@@ -122,6 +140,7 @@ starter:
 		if emojiLength := matchFullyQualifiedEmoji(source[pos:]); emojiLength > 0 {
 			value = append(value, source[pos:pos+emojiLength]...)
 			pos += emojiLength
+			previousWasXIDContinuation = false
 			continue
 		}
 		r, size := utf8.DecodeRune(source[pos:])
@@ -131,9 +150,15 @@ starter:
 		switch {
 		case isDefaultIgnorable(r):
 			pos += size
+			previousWasXIDContinuation = false
+		case isApostropheJoiner(r) && previousWasXIDContinuation && startsNonCombiningXIDContinuation(source[pos+size:]):
+			value = append(value, source[pos:pos+size]...)
+			pos += size
+			previousWasXIDContinuation = false
 		case isSegmentContinuation(r):
 			value = append(value, source[pos:pos+size]...)
 			pos += size
+			previousWasXIDContinuation = isXIDContinue(r) && !isDefaultIgnorable(r)
 		default:
 			return pos, value, true
 		}

internal/markdown/parser/tag_test.go

@@ -222,6 +222,18 @@ func TestFindTagMatchesMemosTagV1(t *testing.T) {
 		{name: "Unicode 16 XID character under Unicode 17 profile", input: "#\u1c89", expectedTag: "\u1c89", expectedSource: "#\u1c89", shouldParse: true},
 		{name: "middle dot XID continue", input: "#l·l", expectedTag: "l·l", expectedSource: "#l·l", shouldParse: true},
 		{name: "connector punctuation XID continue", input: "#foo‿bar", expectedTag: "foo‿bar", expectedSource: "#foo‿bar", shouldParse: true},
+		{name: "ASCII apostrophe joiner", input: "#tag's", expectedTag: "tag's", expectedSource: "#tag's", shouldParse: true},
+		{name: "ASCII apostrophe in Ukrainian", input: "#сім'я", expectedTag: "сім'я", expectedSource: "#сім'я", shouldParse: true},
+		{name: "right curly apostrophe joiner", input: "#O’Brien", expectedTag: "O’Brien", expectedSource: "#O’Brien", shouldParse: true},
+		{name: "modifier letter apostrophe stays XID", input: "#OʼBrien", expectedTag: "OʼBrien", expectedSource: "#OʼBrien", shouldParse: true},
+		{name: "combining mark before apostrophe", input: "#cafe\u0301's", expectedTag: "cafe\u0301's", expectedSource: "#cafe\u0301's", shouldParse: true},
+		{name: "apostrophe cannot start", input: "#'tag", shouldParse: false},
+		{name: "apostrophe cannot end", input: "#users'", expectedTag: "users", expectedSource: "#users", expectedRest: "'", shouldParse: true},
+		{name: "apostrophe cannot repeat", input: "#rock''roll", expectedTag: "rock", expectedSource: "#rock", expectedRest: "''roll", shouldParse: true},
+		{name: "left curly quote terminates", input: "#O‘Brien", expectedTag: "O", expectedSource: "#O", expectedRest: "‘Brien", shouldParse: true},
+		{name: "apostrophe does not adjoin extension", input: "#foo-'bar", expectedTag: "foo-", expectedSource: "#foo-", expectedRest: "'bar", shouldParse: true},
+		{name: "apostrophe does not adjoin fully qualified emoji", input: "#foo'1️⃣", expectedTag: "foo", expectedSource: "#foo", expectedRest: "'1️⃣", shouldParse: true},
+		{name: "apostrophe does not join across ignored code point", input: "#A\u200d'B", expectedTag: "A", expectedSource: "#A\u200d", expectedRest: "'B", shouldParse: true},
 		{name: "currency terminates", input: "#price€", expectedTag: "price", expectedSource: "#price", expectedRest: "€", shouldParse: true},
 		{name: "currency cannot start", input: "#€budget", shouldParse: false},
 		{name: "other number terminates", input: "#v²", expectedTag: "v", expectedSource: "#v", expectedRest: "²", shouldParse: true},

web/src/utils/tag-grammar.ts

@@ -89,6 +89,16 @@ function isExtensionUnit(value: string): boolean {
   return value === "-" || value === "+" || value === "&";
 }
 
+function isApostropheJoiner(value: string): boolean {
+  return value === "'" || value === "’";
+}
+
+function isNonCombiningXIDContinuationAt(source: string, index: number, limit: number): boolean {
+  if (index >= limit || emojiAt(source, index, limit)) return false;
+  const value = codePointAt(source, index);
+  return index + value.length <= limit && isXIDContinue(value) && !isCombiningMark(value);
+}
+
 interface SegmentMatch {
   to: number;
   value: string;
@@ -109,6 +119,7 @@ function scanSegment(source: string, from: number, limit: number): SegmentMatch
   }
 
   let value = "";
+  let previousWasXIDContinuation = false;
   const starterEmoji = emojiAt(source, index, limit);
   if (starterEmoji) {
     value = starterEmoji;
@@ -118,6 +129,7 @@ function scanSegment(source: string, from: number, limit: number): SegmentMatch
     if (!starter || (!(isXIDContinue(starter) && !isCombiningMark(starter)) && !isExtensionUnit(starter))) return undefined;
     value = starter;
     index += starter.length;
+    previousWasXIDContinuation = isXIDContinue(starter);
   }
 
   while (index < limit) {
@@ -125,17 +137,30 @@ function scanSegment(source: string, from: number, limit: number): SegmentMatch
     if (emoji) {
       value += emoji;
       index += emoji.length;
+      previousWasXIDContinuation = false;
       continue;
     }
 
     const codePoint = codePointAt(source, index);
     if (isDefaultIgnorable(codePoint)) {
       index += codePoint.length;
+      previousWasXIDContinuation = false;
+      continue;
+    }
+    if (
+      isApostropheJoiner(codePoint) &&
+      previousWasXIDContinuation &&
+      isNonCombiningXIDContinuationAt(source, index + codePoint.length, limit)
+    ) {
+      value += codePoint;
+      index += codePoint.length;
+      previousWasXIDContinuation = false;
       continue;
     }
     if (isXIDContinue(codePoint) || isExtensionUnit(codePoint)) {
       value += codePoint;
       index += codePoint.length;
+      previousWasXIDContinuation = isXIDContinue(codePoint);
       continue;
     }
     break;

web/tests/editor-decorations.test.ts

@@ -21,6 +21,17 @@ function countClass(doc: string, cls: string): number {
 describe("tag/mention decorations", () => {
   it("decorates #tags", () => expect(countClass("a #todo and #work/sub b", "cm-memo-tag")).toBe(2));
   it("does not require a left boundary", () => expect(countClass("hello#tag 中文#标签", "cm-memo-tag")).toBe(2));
+  it("keeps apostrophes only inside XID words", () => {
+    const source = "#tag's #сім'я #O’Brien '#quoted' #users' #'missing";
+    const state = EditorState.create({ doc: source, extensions: [markdown({ extensions: memoMarkdownExtensions })] });
+    expect(findMarkdownTagMatches(state, 0, source.length).map(({ source, value }) => ({ source, value }))).toEqual([
+      { source: "tag's", value: "tag's" },
+      { source: "сім'я", value: "сім'я" },
+      { source: "O’Brien", value: "O’Brien" },
+      { source: "quoted", value: "quoted" },
+      { source: "users", value: "users" },
+    ]);
+  });
   it("uses emitted spans for ignored characters and emoji", () =>
     expect(countClass("#A‍B #́foo #foo/́bar #👩‍💻 #️⃣ ##️⃣", "cm-memo-tag")).toBe(5));
   it("keeps maximal valid prefixes and adjacent tags", () =>

web/tests/editor-tag-autocomplete.test.ts

@@ -38,6 +38,16 @@ describe("tag autocomplete", () => {
     expect(result?.options.map((option) => option.label)).toEqual(["AB"]);
   });
 
+  it("completes tags containing word-internal apostrophes", () => {
+    const ascii = complete("#O'Br", 5, ["O'Brien", "O’Connor"]);
+    expect(ascii?.from).toBe(1);
+    expect(ascii?.options.map((option) => option.label)).toEqual(["O'Brien"]);
+
+    const curly = complete("#O’Co", 5, ["O'Brien", "O’Connor"]);
+    expect(curly?.from).toBe(1);
+    expect(curly?.options.map((option) => option.label)).toEqual(["O’Connor"]);
+  });
+
   it("keeps unknown character-reference shapes in literal tag source", () => {
     const source = "#R&bogus;D";
     const position = source.indexOf(";");

web/tests/remark-tag.test.tsx

@@ -534,6 +534,16 @@ describe("remarkMemoSyntax", () => {
     expect(html).toContain('data-tag="👩‍💻"');
   });
 
+  it("keeps word-internal apostrophes without absorbing quotation punctuation", () => {
+    const html = renderMarkdown("#tag's #сім'я #O’Brien '#quoted' #users'");
+
+    expect(html).toContain('<span class="tag" data-tag="tag&#x27;s">#tag&#x27;s</span>');
+    expect(html).toContain('<span class="tag" data-tag="сім&#x27;я">#сім&#x27;я</span>');
+    expect(html).toContain('<span class="tag" data-tag="O’Brien">#O’Brien</span>');
+    expect(html).toContain('&#x27;<span class="tag" data-tag="quoted">#quoted</span>&#x27;');
+    expect(html).toContain('<span class="tag" data-tag="users">#users</span>&#x27;');
+  });
+
   it("uses maximal-prefix hierarchy and adjacent-introducer rules", () => {
     const html = renderMarkdown("#book/ #book//fiction #first#second ##tag #️⃣ ##️⃣");
 

web/tests/tag-grammar.test.ts

@@ -18,6 +18,10 @@ describe("tag scanner", () => {
     ["#book//fiction", ["book"]],
     ["#book/fiction/", ["book/fiction"]],
     ["#l·l #foo‿bar", ["l·l", "foo‿bar"]],
+    ["#tag's #сім'я #O'Brien #O’Brien #OʼBrien", ["tag's", "сім'я", "O'Brien", "O’Brien", "OʼBrien"]],
+    ["#café's", ["café's"]],
+    ["'#tag' #users' #'missing #rock''roll", ["tag", "users", "rock"]],
+    ["#O‘Brien #foo-'bar #foo'1️⃣ #A‍'B", ["O", "foo-", "foo", "A"]],
     ["#foo,bar #price€ #€budget #v²", ["foo", "price", "v"]],
     ["#first#second", ["first", "second"]],
     ["##tag", ["tag"]],
@@ -50,4 +54,8 @@ describe("tag scanner", () => {
   it("does not match an emoji across the requested source limit", () => {
     expect(findTagMatches("#😀", 0, 2)).toEqual([]);
   });
+
+  it("does not join an apostrophe across the requested source limit", () => {
+    expect(findTagMatches("#O'B", 0, 3).map((match) => match.value)).toEqual(["O"]);
+  });
 });