Update MD051/link-fragments to allow HTML's implicit "#top" fragment (fixes #1488).

doc-build/md051.md

@@ -52,6 +52,13 @@ attribute can be used to define a fragment:
 An `a` tag can be useful in scenarios where a heading is not appropriate or for
 control over the text of the fragment identifier.
 
+[HTML links to `#top` scroll to the top of a document][html-top-fragment]. This
+rule allows that syntax (using lower-case for consistency):
+
+```markdown
+[Link](#top)
+```
+
 This rule also recognizes the custom fragment syntax used by GitHub to highlight
 [specific content in a document][github-linking-to-content].
 
@@ -81,3 +88,4 @@ append an incrementing integer as needed for uniqueness.
 [github-section-links]: https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#section-links
 [github-heading-algorithm]: https://github.com/gjtorikian/html-pipeline/blob/f13a1534cb650ba17af400d1acd3a22c28004c09/lib/html/pipeline/toc_filter.rb
 [github-linking-to-content]: https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/creating-a-permanent-link-to-a-code-snippet#linking-to-markdown#linking-to-markdown
+[html-top-fragment]: https://html.spec.whatwg.org/multipage/browsing-the-web.html#scrolling-to-a-fragment

doc/Rules.md

@@ -2198,6 +2198,13 @@ attribute can be used to define a fragment:
 An `a` tag can be useful in scenarios where a heading is not appropriate or for
 control over the text of the fragment identifier.
 
+[HTML links to `#top` scroll to the top of a document][html-top-fragment]. This
+rule allows that syntax (using lower-case for consistency):
+
+```markdown
+[Link](#top)
+```
+
 This rule also recognizes the custom fragment syntax used by GitHub to highlight
 [specific content in a document][github-linking-to-content].
 
@@ -2227,6 +2234,7 @@ append an incrementing integer as needed for uniqueness.
 [github-section-links]: https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#section-links
 [github-heading-algorithm]: https://github.com/gjtorikian/html-pipeline/blob/f13a1534cb650ba17af400d1acd3a22c28004c09/lib/html/pipeline/toc_filter.rb
 [github-linking-to-content]: https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/creating-a-permanent-link-to-a-code-snippet#linking-to-markdown#linking-to-markdown
+[html-top-fragment]: https://html.spec.whatwg.org/multipage/browsing-the-web.html#scrolling-to-a-fragment
 
 <a name="md052"></a>
 

doc/md051.md

@@ -64,6 +64,13 @@ attribute can be used to define a fragment:
 An `a` tag can be useful in scenarios where a heading is not appropriate or for
 control over the text of the fragment identifier.
 
+[HTML links to `#top` scroll to the top of a document][html-top-fragment]. This
+rule allows that syntax (using lower-case for consistency):
+
+```markdown
+[Link](#top)
+```
+
 This rule also recognizes the custom fragment syntax used by GitHub to highlight
 [specific content in a document][github-linking-to-content].
 
@@ -93,3 +100,4 @@ append an incrementing integer as needed for uniqueness.
 [github-section-links]: https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#section-links
 [github-heading-algorithm]: https://github.com/gjtorikian/html-pipeline/blob/f13a1534cb650ba17af400d1acd3a22c28004c09/lib/html/pipeline/toc_filter.rb
 [github-linking-to-content]: https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/creating-a-permanent-link-to-a-code-snippet#linking-to-markdown#linking-to-markdown
+[html-top-fragment]: https://html.spec.whatwg.org/multipage/browsing-the-web.html#scrolling-to-a-fragment

lib/md051.mjs

@@ -66,7 +66,8 @@ export default {
   "parser": "micromark",
   "function": function MD051(params, onError) {
     const ignoreCase = params.config.ignore_case || false;
-    const fragments = new Map();
+    /** @type {Map<string, number>} */
+    const fragments = new Map([ [ "#top", 0 ] ]);
 
     // Process headings
     const headingTexts = filterByTypesCached([ "atxHeadingText", "setextHeadingText" ]);

test/link-fragments.md

@@ -332,6 +332,12 @@ Valid Setext Heading with Named Fragment {#setext}
 
 [Invalid](#C11-L4C31) {MD051}
 
+## Implicit Fragments
+
+[Valid](#top)
+
+[Invalid](#ToP) {MD051}
+
 <!-- markdownlint-configure-file {
   "emphasis-style": false,
   "heading-style": false,

test/snapshots/markdownlint-test-scenarios.mjs.md

@@ -25749,6 +25749,26 @@ Generated by [AVA](https://avajs.dev).
             'link-fragments',
           ],
         },
+        {
+          errorContext: '[Invalid](#ToP)',
+          errorDetail: 'Expected: #top; Actual: #ToP',
+          errorRange: [
+            1,
+            15,
+          ],
+          fixInfo: {
+            deleteCount: 4,
+            editColumn: 11,
+            insertText: '#top',
+          },
+          lineNumber: 339,
+          ruleDescription: 'Link fragments should be valid',
+          ruleInformation: 'https://github.com/DavidAnson/markdownlint/blob/v0.0.0/doc/md051.md',
+          ruleNames: [
+            'MD051',
+            'link-fragments',
+          ],
+        },
       ],
       fixed: `# Valid/Invalid Link Fragments␊
       ␊
@@ -26084,6 +26104,12 @@ Generated by [AVA](https://avajs.dev).
       ␊
       [Invalid](#C11-L4C31) {MD051}␊
       ␊
+      ## Implicit Fragments␊
+      ␊
+      [Valid](#top)␊
+      ␊
+      [Invalid](#top) {MD051}␊
+      ␊
       <!-- markdownlint-configure-file {␊
         "emphasis-style": false,␊
         "heading-style": false,␊