Code highlighting

Foldocs highlights fenced code during compilation with Shiki's GitHub light and dark themes. Highlighted HTML contains accessible visual line numbers without injecting numbers into copied source text.

Custom highlighter

Pass highlightCode when another service or language engine should own the output:

import { type CodeHighlighter, compile } from 'foldocs-mdx'

const highlightCode: CodeHighlighter = async input => {
  if (input.language !== 'custom') return undefined
  return renderCustomLanguage(input.value)
}

await compile(source, { filePath, highlightCode })

Returning undefined falls back to the built-in highlighter. Set highlight: false when the consumer only needs the normalized AST.

Twoslash is provided separately by @foldocs/twoslash for compiler-powered TypeScript hovers.