from-this.php

       // Checks that all of the fields are present and not null
        if (isset($_POST['username'], $_POST['email'], $_POST['password'])
            && !String::isEmpty($_POST['username'], $_POST['email'], $_POST['password']))
        {
            // Checks that the username is the correct format
            if (strlen($_POST['username']) > 32)
            {
                $message = 'Usernames may not be more than 32 characters.';
            }
            elseif (!preg_match('/^[a-z0-9-]+$/i', $_POST['username']))
            {
                $message = 'Usernames may only contain alphanumeric characters or dashes.';
            }
            elseif (substr($_POST['username'], 0, 1) == '-' || substr($_POST['username'], -1, 1) == '-')
            {
                $message = 'Usernames may not start or end with a dash.';
            }
            elseif (preg_match('/-{2,}/', $_POST['username']))
            {
                $message = 'Usernames may not have two or more dashes in a row.';
            }
            // Checks that the email address is the correct format
            elseif (!filter_var($_POST['email'], FILTER_VALIDATE_EMAIL))
            {
                $message = 'Your email address is invalid.';
            }
            // Checks that the password is at least 8 characters
            elseif (strlen($_POST['password']) < 6)
            {
                $message = 'Passwords may not be less than 8 characters.';
            }
            else
            { ... }

to-this.php

    protected $ajax   = true;
    protected $method = 'POST';

    protected $validate = array(
        'username' => array(
            'length:>:32'             => 'Usernames may not be more than 32 characters.',
            'regex:is:/[^a-z0-9-]+/i' => 'Usernames may only contain alphanumeric characters or dashes.',
            'regex:is:/^(-.+|.+-)$/'  => 'Usernames may not start or end with a dash.',
            'regex:is:/-{2,}/'        => 'Usernames may not have two or more dashes in a row.',
        ),
        'email' => array(
            'filter:email'         => 'Your email address is invalid.',
        ),
        'password' => array(
            'length:<:8'           => 'Passwords may not be less than 8 characters.',
        ),
    );