Function mdbook::utils::take_rustdoc_include_lines

pub fn take_rustdoc_include_lines<R: RangeBounds<usize>>(
    s: &str, 
    range: R
) -> String

Keep lines contained within the range specified as-is. For any lines not in the range, include them but use # at the beginning. This will hide the lines from initial display but include them when expanding the code snippet or testing with rustdoc.