[BCLASS and $CLASS are both synonyms for __PACKAGE__. Easier to type.

$CLASS has the additional benefit of working in strings.

CLASS is a constant, not a subroutine call. $CLASS is a plain variable, it is
not tied. There is no performance loss for using CLASS over __PACKAGE__ except
the loading of the module.

WWW: http://search.cpan.org/dist/CLASS/