User
Usernames
Valid usernames must not be empty and contain only:
alphanumeric characters (0...9, a...z, A...Z)
_
.
Valid usernames must not contain:
blank spaces
special characters
Examples
Username
is valid
username
true
user.name
true
user_name
true
123username
true
MyUsername
true
(blank space)
false
(empty)
false
user name
false
não_válido
false
user:name
false
user@email.com
false