RegEx = Regular Expression
Some very simple regular expressions to limit the usernames are:
- /^[a-z]+$/i (only alphabets allowed)
- /^[a-z\s]+$/i (alphabets & spaces allowed)
- /^[a-z0-9]+$/i (alphanumeric characters only)
- /^[a-z0-9\s]+$/i (alphanumeric & spaces)