create username with dots

[lbf1]

at 'Users > Add New' its not possible to create users with '.' in the name, but in Network Admin > Users > Add New its possible...

(normal) wp-includes/ms-functions.php

function wpmu_validate_user_signup($user_name, $user_email) {
...
	preg_match( '/[a-z0-9]+/', $user_name, $maybe );
...
}
Only lowercase letters (a-z) and numbers are allowed.

(network) wp-admin/network/user-new.php
dont have any regexp...

Non-Multisite uses only ​sanitize_user with $strict = true and Multisite first uses wpmu_validate_user_signup.

I think dots aren't allowed because it's used for the site domain name too.

So which way do we want to standardize? Allowing dots or not?

Not allowing dots is a holdover from when the user name and domain were one and the same. That said, for now let's make network/user-new.php use wpmu_validate_user_signup(). In a later release we can drop the dot stripping.

Use wpmu_validate_user_signup() in network/user-new.php

In [18131]:

Make user validation when adding a user via network admin consistent with adding a user elsewhere. Provide better feedback for validation problems. Props sorich87. fixes #17239