Digit map syntax question

Hello

I have question about megaco digit map syntax.
Is digitmap, like "([0-9ef])" valid?
I use erlang OTP megaco stack, and it interpretes this digit map that
following numbers is valid:
"0ef", "1ef", "2ef" etc.
Is it right or there is error in megaco stack? I think that valid
number values must be:
"0", "1", "2", ..., "9", "e", "f"

Say me please, which method is right?

-- 
Maxim Treskin