Contains combinator that you can use to control loop, valid data and more. Like you want as many `i` as possible `is(b'i').fold_bounds(.., || (), Acc::acc)`. When you get used to it this `fold_bounds` do everything you need.
Combinator about branching: [Utils::and], [Utils::or].
Combinator about looping: [Utils::fold_bounds] (and rest of fold family), [Utils::fill].
Combinator often used: [Utils::opt], [Utils::map], [Utils::span].