zero to make two). These restrictions are to lower the incidence of
typos causing the class to not match what you thought it would.
+If a regular bracketed character class contains a C<\p{}> or C<\P{}> and
+is matched against a non-Unicode code point, a warning may be
+raised, as the result is not Unicode-defined. No such warning will come
+when using this extended form.
+
The final difference between regular bracketed character classes and
these, is that it is not possible to get these to match a
multi-character fold. Thus,