Use this to dynamically register postfilters to run templates through after they are compiled. See template postfilters for more information on how to setup a postfiltering function.
The php-function callback function can be either (a) a string containing the function name or (b) an array of the form array(&$object, $method) with &$object being a reference to an object and $method being a string containing the mehod-name or (c) an array of the form array(&$class, $method) with $class being a classname and $method being a class method of that class.