Personally, I'd do ... unless UNIVERSAL::isa($self, __PACKAGE__);, but that's just me.

As for your ideas re: attributes ... they're good ideas. Come up with something, test it it, then submit it to CPAN for the community to use. *grins* It's the best thing about open-source!

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We are the carpenters and bricklayers of the Information Age.

Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.