In O'Reilly's Perl Hacks you'll find a similar issue with an attribute Doc for docstrings living in UNIVERSAL.

Maybe we just need a module to safely add features to UNIVERSAL and warn about conflicts.

> my %capital : Hash::Sorted;

> would be too cumbersome.

really?

Maybe just leave it to the user. An import-option could specify the namespace.

I wouldn't mind having different modules collecting their attributes into X:: like "eXtension".

Why not X::Sorted or X::Doc ... or _::Sorted or _::Doc? :)

BTW: Happy to find other's trying to use syntactic sugar to extend the language! =)