Development record

unresolvableFrontmatterShape and the setext first-block bound run on the first --- found anywhere, so a frontmatter-less admitted doc with a thematic break refuses the whole assembly (a lone rule reads as an unclosed block; a rule followed by an image line reads as a YAML tag; a rule followed by an anchor-like line or a dots paragraph likewise); every docs page is admitted and several open with image lines. Scope both to a block opening at line 0 (BOM allowed), which is the only place the stripper recognises one. Residue, pre-existing and shared with the site renderer: a four-space-indented fence delimiter is accepted as a fence while CommonMark reads an indented code block, so a heading between two such lines is masked.