Function continued_depth 

pub fn continued_depth(
    line: &str,
    enclosing: &[Enclosure],
    item_runs: &[usize],
) -> usize

How many of the containers in enclosing (outermost first) line continues: the longest prefix of enclosing that strip_enclosure accepts.

item_runs is item_runs(enclosing). Once the rest of the line is blank, the items up to the next quote continue it and that quote does not, so the cost is bounded by the line’s length rather than by the nesting depth.