Patrones de nombre de usuario
Only letters (either case), numbers, and the underscore; no more than 15 characters. [A-Za-z0-9_]{1,15}
Excited Elk
Only letters (either case), numbers, and the underscore; no more than 15 characters. [A-Za-z0-9_]{1,15} Only letters (either case), numbers, hyphens, underscores, and periods. (Not the slash character, that is being used to escape the period.) The username must start with a letter and must be between 1 and 20 characters long (inclusive). [a-zA-Z][a-zA-Z0-9-_.]{1,20} Only lowercase letters and numbers; at least 5 characters, but no limit. [a-zd.]{5,}