Identifiers are usually of the form

identifier: idfirst idcont*
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For example, identifiers can usually contain digits, but not in the first position.

It sounds like Perl6 will allow

identifier: idfirst idcont* ( [-'] idfirst idcont* )*
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What is it and is it current?

Actually, identifiers aren't well defined in Perl5. Tom Christiansen tried to hammer down the definition on p5p in the last two weeks, but I didn't follow the conversation. I'll locate it if you ask.