Expose Markdown validation selection

docs/consumers/publish.md

@@ -78,6 +78,19 @@ blob size is its link text; gitlinks are omitted. This check measures only the
 captured candidate and reports one oversized file with its measurement as
 `file-size`; it stops publication before product checks or tag creation.
 
+Set `Validation.Markdown` to check committed local Markdown destinations and
+supported heading fragments during publication. Nil disables the check; an
+empty object enables it with outside-checkout links reported as out of scope.
+Set `EnforceCheckoutBoundary` to fail those links. Submodule contents remain
+out of scope under either setting. Observations use the request's output writer;
+failures use `markdown-links` and stop publication before product checks or tag
+creation.
+
+ReleaseKit-owned selections replace duplicate generic suite, vet, formatting,
+distribution, and Markdown checks in configured product checks. Keep
+release-note rules and consumer-specific assertions, such as maintained-example
+tests, in `AdditionalChecks` or profile `checks`.
+
 If `Build` selects targets, ReleaseKit verifies them after the standard suite
 and additional checks, before creating the tag. The operation then rechecks the
 candidate and remote guards, creates an annotated tag for the captured commit,