When hinting at the format for strict data entry in a textbox on a website (
<input type="text"/>), I normally use
A to represent alphabetic characters, and
9 for numeric characters.
AA999 would signify that things like
xy221 would be accepted.
But is there a standard way to state that you can enter an alphanumeric character (i.e.
[a-zA-Z0-9] in regex)?