fix: Markdown.ToMd serialises AnchorLink as inline HTML anchor

Previously AnchorLink spans were silently dropped (rendered as "").
Named anchors are now emitted as <a name="..."></a> inline HTML
so they survive a ToMd round-trip and remain functional when the
output is later converted to HTML.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

RELEASE_NOTES.md

@@ -20,6 +20,7 @@
 * Remove stray `printfn` debug output emitted to stdout when `Markdown.ToMd` encountered an unrecognised paragraph type.
 * Fix `Markdown.ToLatex` producing invalid LaTeX output for level-6 (and deeper) headings. Previously the LaTeX command was an empty string, resulting in bare `{content}` without a command prefix. Headings at level 6+ are now serialised as `\subparagraph{...}`, which is the deepest sectioning command available in LaTeX.
 * Fix `Markdown.ToMd` serialising unresolved indirect links as `[body](key)` (treating the reference key as a URL) instead of the correct `[body][key]` form. Unresolved indirect links are now preserved in their original indirect-reference form, consistent with how unresolved indirect images are handled.
+* Fix `Markdown.ToMd` silently dropping `AnchorLink` spans. Named anchors (used by the API documentation generator to create in-page navigation targets) are now serialised as `<a name="..."></a>` inline HTML, so they survive a round-trip and remain functional when the output is later converted to HTML.
 
 ### Added
 * Introduce `--panel-background` and `--panel-border` CSS custom properties in `fsdocs-default.css`. These decouple panel/component colours (copy-code button, blockquotes, sidebar, page menu, dialogs, tooltips, API tables) from `--header-background`/`--header-border`. Both variables default to the header values, so existing themes are unaffected; themes that need a different colour for content panels can now override `--panel-background` and `--panel-border` independently. [#1156](https://github.com/fsprojects/FSharp.Formatting/issues/1156)

src/FSharp.Formatting.Markdown/MarkdownUtils.fs

@@ -104,7 +104,7 @@ module internal MarkdownUtils =
         | Literal(str, _) -> str
         | HardLineBreak(_) -> "  " + ctx.Newline
 
-        | AnchorLink _ -> ""
+        | AnchorLink(link, _) -> sprintf "<a name=\"%s\"></a>" link
         | DirectLink(body, link, title, _) ->
             let t =
                 title

tests/FSharp.Markdown.Tests/Markdown.fs

@@ -2056,3 +2056,20 @@ let ``ToMd serialises single-line equation block as compact dollar-dollar notati
     let result = Markdown.ToMd(doc, newline = "\n")
     result |> should contain "$$E = mc^2$$"
     result |> should not' (contain "\\begin{equation}")
+
+[<Test>]
+let ``ToMd serialises AnchorLink as inline HTML anchor`` () =
+    // AnchorLink spans must not be silently dropped — they should be emitted as <a name="…"></a>
+    // so that named anchors survive a ToMd round-trip and remain functional when later converted to HTML.
+    let doc =
+        MarkdownDocument(
+            [ Paragraph(
+                  [ AnchorLink("my-anchor", MarkdownRange.zero); Literal("text", MarkdownRange.zero) ],
+                  MarkdownRange.zero
+              ) ],
+            dict []
+        )
+
+    let result = Markdown.ToMd(doc, newline = "\n")
+    result |> should contain "<a name=\"my-anchor\"></a>"
+    result |> should contain "text"