HTML_QuickForm::registerRule()

Name of validation rule

Either: 'regex' or 'callback' ('function' is also kept for backward compatibility). If registering a subclass of HTML_QuickForm_Rule you can pass anything here, preferrably NULL or empty string.

Name of function, regular expression, classname of HTML_QuickForm_Rule subclass or an instance of such class.

Object parent of above function, name of the file containing the subclass of HTML_QuickForm_Rule.