Function scan_html_comments 

pub fn scan_html_comments(
    content: &str,
    code_span_ranges: &[(usize, usize)],
    code_block_ranges: &[(usize, usize)],
    scan_from: usize,
) -> HtmlCommentScan

Scan for HTML comments, keeping the position of an opener that never closes.

Same scan as compute_html_comment_ranges_filtered, which discards the unterminated opener. MD086 reports it, so it is carried out of the scan rather than re-derived by a second, possibly disagreeing pass.

scan_from is the byte offset the document’s body starts at, so front matter can be excluded. A <!-- in a YAML or TOML value is data, and pairing it with a --> in the body would mark everything in between as a comment, hiding it from every rule.