The biggest problem is that use locale and use utf8 are scoped to the enclosing block, contrary to strict.

I define an XML name to be my $REG_NAME= q{[^\W\d_][\w:.-]*}; and when I match a name, in different places in the module, I'd like the \W and \w to use the locale/utf8 pragma, depending on a variable set by the user.

The solutions I can think of are: testing everywhere I match (a pain, and it means duplicating code) or create a method that would just do the match (but it would actually have to be several methods, one for each regexp in which I use $REG_NAME, plus it will probably impact the performaces, I have to assess this). It is easier when the match is done through a dynamically generated function, because I can include the use in the text of the function.