Period in login name?

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It is common these days to see a period in a login name or email address, such as John.Smith or J.Smith. However, c5 only allows letters and digits (and spaces, if you define a constant).

Is there a particular reason why periods are not allowed? Is there some kind of conflict in the code? Were periods not common when the name check was written? Is it a readability issue? Is it fine to use a period and someone just needs to submit a patch to make it work?

mose