"Usernames must start with a letter, only lowercase letters and numbers are allowed, and cannot end with an underscore.
A username can contain letters, numbers and underscore. It cannot contain spaces, -, . and non-alphanumeric characters."
‘only lowercase letters and numbers are allowed’ conflicts with ‘can contain… underscore’
When I type e.g. ‘happiest’, it’s green. When I type ‘happiest_’, it becomes orange/red. However, when I type e.g. ‘happiest_elephant’, it stays orange/red and refuses the username.