"Pcrecompat man page" says:
> 5. The following Perl escape sequences are not supported: \l, \u, \L,
> \U, and \N. In fact these are implemented by Perl's general
> string-handling and are not part of its pattern matching engine. If any
> of these are encountered by PCRE, an error is generated.
\N semantics is described in "pcrepattern man page" and this escape
sequence is not generate an error.
