</code></h3>
<p>
Creates a <em>match-time capture</em>.
Unlike all other captures,
this one is evaluated immediately when a match occurs.
It forces the immediate evaluation of all its nested captures
and then calls <code>function</code>.
</p>

<p>
The given function gets as arguments the entire subject,
the current position (after the match of <code>patt</code>),
plus any capture values produced by <code>patt</code>.
</p>

<p>
The first value returned by <code>function</code>
defines how the match happens.
