The Zend_Filter component provides a set of commonly needed data filters. It also provides a simple filter chaining mechanism by which multiple filters may be applied to a single datum in a user-defined order.
Alnum – Zend_Filter_Alnum is a filter which returns only alphabetic characters and digits. All other characters are supressed.
Alpha – Zend_Filter_Alpha is a filter which returns the string $value, removing all but alphabetic characters. This filter includes an option to also allow white space characters.