I>Index</I> indicates which of several ranges is desired:
if <I>index</I> is 0, information is returned about the overall range
of characters that matched the entire pattern;  otherwise,
information is returned about the range of characters that matched the
<I>index</I>'th parenthesized subexpression within the pattern.
If there is no range corresponding to <I>index</I> then NULL
is stored in <I>*startPtr</I> and <I>*endPtr</I>.
<P>
<B>Tcl_GetRegExpFromObj</B>, <B>Tcl_RegExpExecObj</B>, and
<B>Tcl_RegExpGet