Preserve code fences in generated text

Delimiter rule

CommonMark fenced code blocks use runs of backticks or tildes. A closing fence uses the same character and must be at least as long as the opening fence. A generator must account for fence-like lines inside the sample.

Proposed generator

Scan the sample for runs of the chosen delimiter. Choose an outer run longer than any potentially closing run in the sample, with a minimum length of three. Keep sample bytes unchanged; do not escape or reindent code merely to make it look safe in Markdown.

Worked case

A sample explains triple-backtick Markdown. Wrap it in four backticks, or use a sufficiently long tilde fence. Put the closing delimiter on its own line. Ensure that an optional language label is validated separately rather than copied from untrusted input.

Acceptance and limits

Parse the generated Markdown using the site's actual renderer and compare the resulting code text with the original sample, allowing only the renderer's documented terminal-newline handling. Test nested fences, empty code and trailing delimiter lines. This is a text-preservation technique, not permission to execute the code or to enable raw HTML in contributed documents.