Update MD051/link-fragments to use the same character classes as GitHub, encode unprintable characters from emojii.

demo/markdownlint-browser.js

@@ -4408,10 +4408,14 @@ var identifierRe = /(?:id|name)\s*=\s*['"]?([^'"\s>]+)/iu;
  */
 function convertHeadingToHTMLFragment(inline) {
     var inlineText = inline.children.map(function (token) { return token.content; }).join("");
-    return "#" + inlineText
+    return "#" + encodeURIComponent(inlineText
         .toLowerCase()
-        .replace(/ /g, "-")
-        .replace(/[^-_a-z0-9]/g, "");
+        // RegExp source with Ruby's \p{Word} expanded into its General Categories
+        // eslint-disable-next-line max-len
+        // https://github.com/gjtorikian/html-pipeline/blob/main/lib/html/pipeline/toc_filter.rb
+        // https://ruby-doc.org/core-3.0.2/Regexp.html
+        .replace(/[^\p{Letter}\p{Mark}\p{Number}\p{Connector_Punctuation}\- ]/gu, "")
+        .replace(/ /gu, "-"));
 }
 module.exports = {
     "names": ["MD051", "link-fragments"],

lib/md051.js

@@ -18,10 +18,19 @@ const identifierRe = /(?:id|name)\s*=\s*['"]?([^'"\s>]+)/iu;
  */
 function convertHeadingToHTMLFragment(inline) {
   const inlineText = inline.children.map((token) => token.content).join("");
-  return "#" + inlineText
-    .toLowerCase()
-    .replace(/ /g, "-")
-    .replace(/[^-_a-z0-9]/g, "");
+  return "#" + encodeURIComponent(
+    inlineText
+      .toLowerCase()
+      // RegExp source with Ruby's \p{Word} expanded into its General Categories
+      // eslint-disable-next-line max-len
+      // https://github.com/gjtorikian/html-pipeline/blob/main/lib/html/pipeline/toc_filter.rb
+      // https://ruby-doc.org/core-3.0.2/Regexp.html
+      .replace(
+        /[^\p{Letter}\p{Mark}\p{Number}\p{Connector_Punctuation}\- ]/gu,
+        ""
+      )
+      .replace(/ /gu, "-")
+  );
 }
 
 module.exports = {

test/link-fragments.md

@@ -18,6 +18,10 @@
 
 [Valid](#valid-heading--with-emoji-2)
 
+[Valid](#valid-heading-2010-)
+
+[Valid](#valid-heading-2004-%EF%B8%8F)
+
 [Valid](#valid-closed-atx-heading)
 
 [Valid](#valid-setext-heading)
@@ -56,6 +60,14 @@ Text
 
 Text
 
+### Valid Heading 20.10 ❌
+
+Text
+
+### Valid Heading 20.04 ✔️
+
+Text
+
 ### Valid Closed ATX Heading ###
 
 Text
@@ -77,6 +89,8 @@ Text
 
 ## Invalid Fragments
 
+[Inalid](#valid-heading-2004-) {MD051}
+
 [Invalid](#invalid-fragment) {MD051}
 
 [Invalid](#myname) {MD051}