 many subexpressions are of interest.  If
<I>nmatches</I> is 0, then no subexpression match information is
recorded, which may allow the matcher to make various optimizations.
If the value is -1, then all of the subexpressions in the pattern are
remembered.  If the value is a positive integer, then only that number
of subexpressions will be remembered.  Matching begins at the
specified Unicode character index given by <I>offset</I>.  Unlike
<B>Tcl_RegExpExec</B>, the behavior of anchors is not affected by t