Moreover, I prefer this regular expression "^[A-Za-z0-9]{4,30}$" than
"^[A-Za-z0-9]+$". "^[A-Za-z0-9]{4,30}$" mean only string, that
contain only alphabet or number, is matched, and it must be longer than
3 characters and shorter than 31 characters.

From siLenTz
Hope that is useful...

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