d
subexpression.  The <I>end</I> index identifies the first character
after the matched subexpression.  If the subexpression matched the
empty string, then <I>start</I> and <I>end</I> will be equal.  If the
subexpression did not participate in the match, then <I>start</I> and
<I>end</I> will be set to -1.
<P>
The <I>extendStart</I> field in <B>Tcl_RegExpInfo</B> is only set if the
<B>TCL_REG_CANMATCH</B> flag was used.  It indicates the first
character in the string where a match could occur.  If a match wa