[[ 0 == [[:IDENT:]]## ]]; print $?
0

That's fine. However, it also accepts 0[a-z]:

[[ 0q == [[:IDENT:]]## ]]; print $?
0

Shouldn't  it be defined something like:

(<->|[A-Za-z_][A-Za-z0-9_]#)? So that it accepts $0, and also var0? but not
0var?

-- 
Best regards,
Sebastian Gniazdowski