Function code_long_check 

pub fn code_long_check(
    text: &str,
    h: &Highlighter,
    tw: u8,
    edits: &[(usize, usize, &str)],
) -> Vec<String>

(tests) line text changed by edits one after the other (bytes a..b of the line then replaced by s): the column checkpoints and the tokens a code editor keeps of a long line, brought along through each change, against a fresh look at the line -> what differs (empty: nothing)