group two set to <tt>"b"</tt>.  All captured input is discarded at the
 beginning of each match.

 <p> Groups beginning with <tt>(?</tt> are pure, <i>non-capturing</i> groups
 that do not capture text and do not count towards the group total.


 <h4> Unicode support </h4>

 <p> This class is in conformance with Level 1 of <a
 href="http://www.unicode.org/reports/tr18/"><i>Unicode Technical
 Standard #18: Unicode Regular Expression Guidelines</i></a>, plus RL2.1
 Canonical Equivalents.

 <p> Unicode escape s