# Markdown support
Texio is a Markdown-only tool. It parses documents using `pulldown-cmark` with
CommonMark behavior and the GitHub Flavored Markdown extensions needed for
tables, task lists, footnotes, and strikethrough.
## Supported section syntax
- ATX headings from `#` through `######`
- Setext level-one and level-two headings
- Nested sections bounded by the next heading at the same or a higher level
- Inline Markdown inside heading titles
- LF and CRLF line endings
- Documents with or without a final newline
Heading-like text inside fenced code blocks and HTML blocks is not treated as a
section boundary. Leading YAML front matter is recognized when it has delimiter
lines and at least one unquoted, top-level key containing only ASCII letters,
digits, hyphens, or underscores. Recognized front matter is preserved and never
rewritten by section operations. A leading thematic break is not mistaken for
front matter.
## Editing guarantees
- Section lookup is case-insensitive for ASCII text.
- A missing heading fails instead of creating a new section.
- Duplicate matching headings fail as ambiguous.
- Replacement changes only the selected section body.
- Line endings follow the target document.
- Writes replace the file atomically, retain its permissions, and preserve
symlinks by updating their targets.
## Current limitations
- Section selection is by visible heading text; path-like selectors for
duplicate headings are not implemented yet.
- Unicode case folding is not implemented.
- Markdown embedded in MDX or other templating languages is outside scope.
- Front matter fields are preserved but are not independently queryable.
- Texio does not format, render, or lint Markdown.