Function is_utility 

pub fn is_utility(name: &str) -> bool

Whether this class is a Tailwind utility Beck knows.

Defined as “there is a rule for it”, which is not a tidiness: a predicate and a generator that could disagree would put a class in a stylesheet with no rule under it, or refuse one the emitter can render — and the first is a page missing a style with every gate green, which is the failure the whole arrangement exists to prevent. There is one table and this reads it.