The format entered for the username must be a string of 1 to 15 characters, composed of the letters A-Z, a-z, 0-9,
'-','_'. The first character may not be numeric.
Explanation:
The format entered for the username must be a string of 1 to 15 characters, composed of the letters A-Z, a-z, 0-9, '-', '_'. The first character may not be numeric.