From 21ab0b6d4bcad03b9cf69b3d43531aa175413d51 Mon Sep 17 00:00:00 2001
From: Nikita Barinov <diadorer@nebius.com>
Date: Tue, 10 Mar 2026 11:13:01 +0100
Subject: [PATCH 01/10] fix: prevent single-tilde strikethrough false positives

When a closing single ~ is followed by an alphanumeric character, skip
the strikethrough match since it fails GFM right-flanking delimiter
rules. This prevents text like `~125 GeV ... **~173 GeV**` from being
incorrectly parsed as strikethrough.
---
 src/Tokenizer.ts                 | 7 +++++++
 test/specs/new/del_flanking.html | 1 +
 test/specs/new/del_flanking.md   | 2 ++
 3 files changed, 10 insertions(+)

diff --git a/src/Tokenizer.ts b/src/Tokenizer.ts
index 1e821e6af8..0eb6e8c20e 100644
--- a/src/Tokenizer.ts
+++ b/src/Tokenizer.ts
@@ -866,6 +866,13 @@ export class _Tokenizer<ParserOutput = string, RendererOutput = string> {
 
         // Create del token - only single ~ or double ~~ supported
         const text = raw.slice(lLength, -lLength);
+
+        // For single ~, skip if closing ~ is followed by an alphanumeric character.
+        // Prevents e.g. `~125 GeV, while the top quark is **~173 GeV**` from matching as strikethrough,
+        // since the closing ~ fails GFM right-flanking delimiter rules.
+        // See https://github.github.com/gfm/#emphasis-and-strong-emphasis
+        if (lLength === 1 && raw.length < src.length && /[0-9a-zA-Z]/.test(src[raw.length])) continue;
+
         return {
           type: 'del',
           raw,
diff --git a/test/specs/new/del_flanking.html b/test/specs/new/del_flanking.html
index f097b7339b..df15a8ca1b 100644
--- a/test/specs/new/del_flanking.html
+++ b/test/specs/new/del_flanking.html
@@ -3,3 +3,4 @@
 <p>Between (~1.34) and (~5.4)</p>
 <p>~ test~</p>
 <p>~test ~</p>
+<p>The mass of the Higgs boson is ~125 GeV, while the top quark is <strong>~173 GeV</strong></p>
diff --git a/test/specs/new/del_flanking.md b/test/specs/new/del_flanking.md
index 9f93a3b388..a06d49e171 100644
--- a/test/specs/new/del_flanking.md
+++ b/test/specs/new/del_flanking.md
@@ -7,3 +7,5 @@ Between (~1.34) and (~5.4)
 ~ test~
 
 ~test ~
+
+The mass of the Higgs boson is ~125 GeV, while the top quark is **~173 GeV**

From a92a300cde8cff60246d9013065082e08e555495 Mon Sep 17 00:00:00 2001
From: Nikita Barinov <diadorer@nebius.com>
Date: Tue, 10 Mar 2026 21:33:37 +0100
Subject: [PATCH 02/10] fix: use unicode alphanumeric check in strikethrough
 delimiter

---
 src/Tokenizer.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Tokenizer.ts b/src/Tokenizer.ts
index 0eb6e8c20e..aafbcba72f 100644
--- a/src/Tokenizer.ts
+++ b/src/Tokenizer.ts
@@ -871,7 +871,7 @@ export class _Tokenizer<ParserOutput = string, RendererOutput = string> {
         // Prevents e.g. `~125 GeV, while the top quark is **~173 GeV**` from matching as strikethrough,
         // since the closing ~ fails GFM right-flanking delimiter rules.
         // See https://github.github.com/gfm/#emphasis-and-strong-emphasis
-        if (lLength === 1 && raw.length < src.length && /[0-9a-zA-Z]/.test(src[raw.length])) continue;
+        if (lLength === 1 && raw.length < src.length && this.rules.other.unicodeAlphaNumeric.test(src[raw.length])) continue;
 
         return {
           type: 'del',

From b5d0a7f4c540fda4be77deb6990ba47926b74be8 Mon Sep 17 00:00:00 2001
From: Nikita Barinov <diadorer@nebius.com>
Date: Wed, 11 Mar 2026 10:22:11 +0100
Subject: [PATCH 03/10] fix: also check char before closing tilde to preserve
 valid strikethrough

---
 src/Tokenizer.ts                      | 12 ++++++++----
 test/specs/new/del_strikethrough.html |  1 +
 test/specs/new/del_strikethrough.md   |  2 ++
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/src/Tokenizer.ts b/src/Tokenizer.ts
index aafbcba72f..49cae662c0 100644
--- a/src/Tokenizer.ts
+++ b/src/Tokenizer.ts
@@ -867,11 +867,15 @@ export class _Tokenizer<ParserOutput = string, RendererOutput = string> {
         // Create del token - only single ~ or double ~~ supported
         const text = raw.slice(lLength, -lLength);
 
-        // For single ~, skip if closing ~ is followed by an alphanumeric character.
-        // Prevents e.g. `~125 GeV, while the top quark is **~173 GeV**` from matching as strikethrough,
-        // since the closing ~ fails GFM right-flanking delimiter rules.
+        // For single ~, skip if closing ~ is not right-flanking per GFM rules:
+        // the closing ~ must be preceded by a non-whitespace, non-punctuation char (alphanumeric)
+        // to be right-flanking. If followed by alphanumeric but NOT preceded by alphanumeric,
+        // it fails the right-flanking delimiter test.
         // See https://github.github.com/gfm/#emphasis-and-strong-emphasis
-        if (lLength === 1 && raw.length < src.length && this.rules.other.unicodeAlphaNumeric.test(src[raw.length])) continue;
+        if (lLength === 1
+          && raw.length < src.length
+          && this.rules.other.unicodeAlphaNumeric.test(src[raw.length])
+          && !this.rules.other.unicodeAlphaNumeric.test(src[raw.length - 2])) continue;
 
         return {
           type: 'del',
diff --git a/test/specs/new/del_strikethrough.html b/test/specs/new/del_strikethrough.html
index 980134aa21..0e25552c54 100644
--- a/test/specs/new/del_strikethrough.html
+++ b/test/specs/new/del_strikethrough.html
@@ -13,4 +13,5 @@
 
 <p>test~~</p>
 
+<p><del>1  a</del>2</p>
 <pre><code class="language-test~~~"></code></pre>
diff --git a/test/specs/new/del_strikethrough.md b/test/specs/new/del_strikethrough.md
index f3d5bca081..d72adfad45 100644
--- a/test/specs/new/del_strikethrough.md
+++ b/test/specs/new/del_strikethrough.md
@@ -13,4 +13,6 @@ test~~
 
 test~~
 
+~1  a~2
+
 ~~~test~~~

From e24034e1767c07a4b06bb048aa71baa11adfcad5 Mon Sep 17 00:00:00 2001
From: Tony Brix <tony@brix.ninja>
Date: Sat, 14 Mar 2026 23:52:54 -0600
Subject: [PATCH 04/10] Refactor strikethrough rule

Removed GFM specific regex patterns for strikethrough and replaced them with general punctuation patterns.
---
 src/rules.ts | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/src/rules.ts b/src/rules.ts
index fd77781ea3..6b1ed33138 100644
--- a/src/rules.ts
+++ b/src/rules.ts
@@ -277,11 +277,6 @@ const _punctuationGfmStrongEm = /(?!~)[\p{P}\p{S}]/u;
 const _punctuationOrSpaceGfmStrongEm = /(?!~)[\s\p{P}\p{S}]/u;
 const _notPunctuationOrSpaceGfmStrongEm = /(?:[^\s\p{P}\p{S}]|~)/u;
 
-// GFM allows * and _ inside strikethrough
-const _punctuationGfmDel = /(?![*_])[\p{P}\p{S}]/u;
-const _punctuationOrSpaceGfmDel = /(?![*_])[\s\p{P}\p{S}]/u;
-const _notPunctuationOrSpaceGfmDel = /(?:[^\s\p{P}\p{S}]|[*_])/u;
-
 // sequences em should skip over [title](link), `code`, <html>
 const blockSkip = edit(/link|precode-code|html/, 'g')
   .replace('link', /\[(?:[^\[\]`]|(?<a>`+)[^`]+\k<a>(?!`))*?\]\((?:\\[\s\S]|[^\\\(\)]|\((?:\\[\s\S]|[^\\\(\)])*\))*\)/)
@@ -338,7 +333,7 @@ const emStrongRDelimUnd = edit(
 
 // Tilde left delimiter for strikethrough (similar to emStrongLDelim for asterisk)
 const delLDelim = edit(/^~~?(?:((?!~)punct)|[^\s~])/, 'u')
-  .replace(/punct/g, _punctuationGfmDel)
+  .replace(/punct/g, _punctuation)
   .getRegex();
 
 // Tilde delimiter patterns for strikethrough (similar to asterisk)
@@ -352,9 +347,9 @@ const delRDelimCore =
 + '|notPunctSpace(~~?)(?=notPunctSpace)'; // (6) a~~a can be either Left or Right Delimiter
 
 const delRDelim = edit(delRDelimCore, 'gu')
-  .replace(/notPunctSpace/g, _notPunctuationOrSpaceGfmDel)
-  .replace(/punctSpace/g, _punctuationOrSpaceGfmDel)
-  .replace(/punct/g, _punctuationGfmDel)
+  .replace(/notPunctSpace/g, _notPunctuationOrSpace)
+  .replace(/punctSpace/g, _punctuationOrSpace)
+  .replace(/punct/g, _punctuation)
   .getRegex();
 
 const anyPunctuation = edit(/\\(punct)/, 'gu')

From aa345863633e608c66dc3ee716674223f72c39ae Mon Sep 17 00:00:00 2001
From: Tony Brix <tony@brix.ninja>
Date: Sat, 14 Mar 2026 23:53:44 -0600
Subject: [PATCH 05/10] Remove tokenizer changes

---
 src/Tokenizer.ts | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/src/Tokenizer.ts b/src/Tokenizer.ts
index 49cae662c0..b7247661f9 100644
--- a/src/Tokenizer.ts
+++ b/src/Tokenizer.ts
@@ -867,16 +867,6 @@ export class _Tokenizer<ParserOutput = string, RendererOutput = string> {
         // Create del token - only single ~ or double ~~ supported
         const text = raw.slice(lLength, -lLength);
 
-        // For single ~, skip if closing ~ is not right-flanking per GFM rules:
-        // the closing ~ must be preceded by a non-whitespace, non-punctuation char (alphanumeric)
-        // to be right-flanking. If followed by alphanumeric but NOT preceded by alphanumeric,
-        // it fails the right-flanking delimiter test.
-        // See https://github.github.com/gfm/#emphasis-and-strong-emphasis
-        if (lLength === 1
-          && raw.length < src.length
-          && this.rules.other.unicodeAlphaNumeric.test(src[raw.length])
-          && !this.rules.other.unicodeAlphaNumeric.test(src[raw.length - 2])) continue;
-
         return {
           type: 'del',
           raw,

From ddf787379ba0d693d09191982d7e576c38abdc13 Mon Sep 17 00:00:00 2001
From: Tony Brix <tony@brix.ninja>
Date: Sat, 14 Mar 2026 23:54:25 -0600
Subject: [PATCH 06/10] Fix formatting in Tokenizer.ts

---
 src/Tokenizer.ts | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/Tokenizer.ts b/src/Tokenizer.ts
index b7247661f9..1e821e6af8 100644
--- a/src/Tokenizer.ts
+++ b/src/Tokenizer.ts
@@ -866,7 +866,6 @@ export class _Tokenizer<ParserOutput = string, RendererOutput = string> {
 
         // Create del token - only single ~ or double ~~ supported
         const text = raw.slice(lLength, -lLength);
-
         return {
           type: 'del',
           raw,

From a720f0008629803fa729683f42f34d541a59c5ca Mon Sep 17 00:00:00 2001
From: Tony Brix <tony@brix.ninja>
Date: Sat, 14 Mar 2026 23:55:18 -0600
Subject: [PATCH 07/10] Update del_strikethrough.md with new test cases

---
 test/specs/new/del_strikethrough.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/test/specs/new/del_strikethrough.md b/test/specs/new/del_strikethrough.md
index d72adfad45..814d5b8d20 100644
--- a/test/specs/new/del_strikethrough.md
+++ b/test/specs/new/del_strikethrough.md
@@ -15,4 +15,6 @@ test~~
 
 ~1  a~2
 
+~~1  a~~2
+
 ~~~test~~~

From 70e380a7d754a93c56612516757740c593c20e62 Mon Sep 17 00:00:00 2001
From: Tony Brix <tony@brix.ninja>
Date: Sat, 14 Mar 2026 23:55:44 -0600
Subject: [PATCH 08/10] Fix strikethrough HTML syntax in del_strikethrough.html

---
 test/specs/new/del_strikethrough.html | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/test/specs/new/del_strikethrough.html b/test/specs/new/del_strikethrough.html
index 0e25552c54..416de2af8c 100644
--- a/test/specs/new/del_strikethrough.html
+++ b/test/specs/new/del_strikethrough.html
@@ -14,4 +14,7 @@
 <p>test~~</p>
 
 <p><del>1  a</del>2</p>
+
+<p><del>1  a</del>2</p>
+
 <pre><code class="language-test~~~"></code></pre>

From 102bda090e1ff7c1127fd16865ff574b48355d2a Mon Sep 17 00:00:00 2001
From: Tony Brix <tony@brix.ninja>
Date: Sat, 14 Mar 2026 23:56:24 -0600
Subject: [PATCH 09/10] Update Higgs boson mass and add new entry

---
 test/specs/new/del_flanking.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/test/specs/new/del_flanking.md b/test/specs/new/del_flanking.md
index a06d49e171..6eeb2981a9 100644
--- a/test/specs/new/del_flanking.md
+++ b/test/specs/new/del_flanking.md
@@ -9,3 +9,5 @@ Between (~1.34) and (~5.4)
 ~test ~
 
 The mass of the Higgs boson is ~125 GeV, while the top quark is **~173 GeV**
+
+~~1 **~~2**

From 350f0635d3bfedd5a6484ca0b269d950e8d7e417 Mon Sep 17 00:00:00 2001
From: Tony Brix <tony@brix.ninja>
Date: Sat, 14 Mar 2026 23:56:53 -0600
Subject: [PATCH 10/10] Add new paragraph with Higgs boson mass details

---
 test/specs/new/del_flanking.html | 1 +
 1 file changed, 1 insertion(+)

diff --git a/test/specs/new/del_flanking.html b/test/specs/new/del_flanking.html
index df15a8ca1b..1cfcec7719 100644
--- a/test/specs/new/del_flanking.html
+++ b/test/specs/new/del_flanking.html
@@ -4,3 +4,4 @@
 <p>~ test~</p>
 <p>~test ~</p>
 <p>The mass of the Higgs boson is ~125 GeV, while the top quark is <strong>~173 GeV</strong></p>
+<p>~~1 <strong>~~2</strong></p>