uring the <em>match time</em> it only gathers enough information
to produce the capture values later.
As a particularly important consequence,
most captures cannot affect the way a pattern matches a subject.
The only exception to this rule is the
so-called <a href="#matchtime"><em>match-time capture</em></a>.
When a match-time capture matches,
it forces the immediate evaluation of all its nested captures
and then calls its corresponding function,
which tells whether the match succeeds and also
what values a