Function code_regions 

pub(crate) fn code_regions(
    text: &str,
    options: &ParseOptions,
) -> Vec<Range<usize>>

Byte ranges that Markdown parses as code under options. An HTML entity would render literally inside these ranges, so neutralization skips them. If malformed MDX cannot be parsed, returning no ranges favors neutralizing possible ESM over preserving an invalid code example byte-for-byte.