Rob Allen has been working with the Zend_Filter component of the Zend Framework and has discovered a few things:

The basic usage of Zend_Filter_Input is [a simple call to Zend_Filter_Input with the filter types and data to filter]. The problem is that the message you get out isn't always written as you would like. Consider the output if the body record is empty. The text isn't exactly what I would want to display to a user. To change it you pass in a messages parameter to the $validators array.

There's a long list of these "messages parameters" and Rob includes them in the post - things like NOT_ALNUM, CHECKSUM, QUOTED_STRING, INVALID_DASH and UNDECIPHERABLE_TLD (37 of them in all).