The string validation is great for validating the user input against a regular expression, or checking the length of the string entered. If you ask for passwords two times to avoid typing mistakes, this validation type will help you to compare the field values.
Below are the dumps of some PHP variables - submit the form to see the changes!
Contents of the $_POST array:
$_POST = array (
)
Results of a $clonefish->getElementValues() call: array ( 'login' => NULL, 'password' => NULL, 'passwordverify' => NULL, 'email' => NULL, 'id' => 'validstring', )