pub fn atx_heading(line: &str) -> Option<(usize, &str)>Expand description
An ATX heading’s level and text: ^ {0,3}(#{1,6})\s+(.+?)\s*$, with a
closing # run stripped when a space or tab precedes it. A bare ## or
## is not a heading; ## (whitespace for text) is one with empty
text, which ends sections but can never be selected.