enh(markdown) add entity support

Author: dschach

CHANGES.md

@@ -28,6 +28,7 @@ Core Grammars:
 - fix(types) fix interface LanguageDetail > keywords [Patrick Chiu]
 - enh(java) add `goto` to be recognized as a keyword in Java [Alvin Joy][]
 - enh(bash) add keyword `sudo` [Alvin Joy][]
+- enh(markdown) add entity support [David Schach][] [TaraLei][]
 
 New Grammars:
 
@@ -62,6 +63,7 @@ Themes:
 [Vitaly Barilko]: https://github.com/Diversus23
 [Patrick Chiu]: https://github.com/patrick-kw-chiu
 [Alvin Joy]: https://github.com/alvinsjoy
+[TaraLei]: https://github.com/TaraLei
 
 
 ## Version 11.9.0

src/languages/markdown.js

@@ -216,6 +216,12 @@ export default function(hljs) {
     end: '$'
   };
 
+  const ENTITY = {
+    //https://spec.commonmark.org/0.31.2/#entity-references
+    scope: 'literal',
+    match: /&([a-zA-Z0-9]+|#[0-9]{1,7}|#[Xx][0-9a-fA-F]{1,6});/
+  };
+
   return {
     name: 'Markdown',
     aliases: [
@@ -233,7 +239,8 @@ export default function(hljs) {
       CODE,
       HORIZONTAL_RULE,
       LINK,
-      LINK_REFERENCE
+      LINK_REFERENCE,
+      ENTITY
     ]
   };
 }

test/markup/markdown/entity.expect.txt

@@ -0,0 +1,3 @@
+<span class="hljs-bullet">-</span> named entities: <span class="hljs-literal">&amp;amp;</span>, <span class="hljs-literal">&amp;frac34;</span>, <span class="hljs-literal">&amp;AElig;</span>
+<span class="hljs-bullet">-</span> decimal entities: <span class="hljs-literal">&amp;#65;</span> <span class="hljs-literal">&amp;#164;</span>
+<span class="hljs-bullet">-</span> hexadecimal entities: <span class="hljs-literal">&amp;#xFFFD;</span> <span class="hljs-literal">&amp;#x48;</span>.

test/markup/markdown/entity.txt

@@ -0,0 +1,3 @@
+- named entities: &, ¾, Æ
+- decimal entities: A ¤
+- hexadecimal entities: � H.