Generate Rules.md and md###.md files from metadata, improve Parameters documentation by referencing schema.

doc/md051.md

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+# MD051 - Link fragments should be valid
+
+Tags: links
+
+Aliases: link-fragments
+
+This rule is triggered when a link fragment does not correspond to a heading
+in the document:
+
+```markdown
+# Title
+
+[Link](#fragment)
+```
+
+To fix the issue, change the fragment to reference an existing heading:
+
+```markdown
+[Link](#title)
+```
+
+Alternatively, an HTML `a` tag with an `id` (or a `name`) attribute defines a
+valid anchor:
+
+```markdown
+<a id="fragment"></a>
+```
+
+Some platforms (e.g., [GitHub][github-section-links]) automatically create HTML
+anchors for every heading. This makes it easy to link to different sections in
+a document. These internal links can break over time as headings are renamed.
+
+Note: Creating anchors for headings is not part of the CommonMark specification.
+
+[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