C<(?#text)>, C<(?imsx-imsx)>, C<(?:pattern)>, C<(?imsx-imsx:pattern)>,
C<(?=pattern)>, C<(?!pattern)>, C<(?E<lt>=pattern)>, C<(?<!pattern)>, C<(?{
-code })>, C<(?p{ code })>, C<(?E<gt>pattern)>,
+code })>, C<(??{ code })>, C<(?E<gt>pattern)>,
C<(?(condition)yes-pattern|no-pattern)>, C<(?(condition)yes-pattern)>
=item Backtracking
C<ST>, C<S|T>, C<S{REPEAT_COUNT}>, C<S{min,max}>, C<S{min,max}?>, C<S?>,
C<S*>, C<S+>, C<S??>, C<S*?>, C<S+?>, C<(?E<gt>S)>, C<(?=S)>, C<(?<=S)>,
-C<(?!S)>, C<(?<!S)>, C<(?p{ EXPR })>,
+C<(?!S)>, C<(?<!S)>, C<(??{ EXPR })>,
C<(?(condition)yes-pattern|no-pattern)>
=item Creating custom RE engines