search time usually requires more "power" that
in turn adds overhead.

Other regex implementations might call capturing groups "submatches."

# Overview

The main types in this module are:

* [`Captures`] records the capturing group offsets found during a search. It
provides convenience routines for looking up capturing group offsets by either
index or name.
* [`GroupInfo`] records the mapping between capturing groups and "slots,"
where the latter are how capturing groups are recorded during a regex search.
This also keeps a mapping from capturing group name to index, and capture
group index to name. A `GroupInfo` is used by `Captures` internally to
provide a convenient API. It is unlikely that you'll use a `GroupInfo`
directly, but for example, if you've compiled an Thompson NFA, then you can use
[`thompson::NFA::group_info`](crate::nfa::thompson::NFA::group_info) to get its
underlying `GroupInfo`.