WordPress at a glance
function is not described

validate_user_form() WP 3.0.0

Validate user signup name and email

No Hooks.

Return

Array. Contains username, email, and error messages.

Usage

validate_user_form();

Code of validate user form: wp-signup.php VER 5.0.3

<?php
function validate_user_form() {
	return wpmu_validate_user_signup($_POST['user_name'], $_POST['user_email']);
}