fn detail_rank(detail: &DetailLevel) -> Option<u8>Expand description
Where detail sits in the levels’ ordering, or None for a level this
crate cannot place.
The levels are a chain — each records everything the one before it does —
so one rank answers every question about which of two a recorder is at.
A level this crate has never heard of has no place in the chain, which is
why this is an Option rather than a number with a default: a default
would guess, and the two ways of guessing wrong are not symmetric.