1).
                  </p>
                  <p>
                    That is to say: the same as <a class="link" href="../../syntax/basic_extended.html" title="POSIX Extended Regular Expression Syntax">POSIX
                    extended syntax</a>, but with escape sequences in character
                    classes permitted.
                  </p>
                  <p>
                    In addition some perl-style escape sequences are supported (actually
                    the awk syntax only requires \a