handler for functional and object-oriented callbacks in Perl

 Params::CallbackRequest provides functional and object-oriented callbacks to
 method and function parameters. Callbacks may be either code references
 provided to the new() constructor, or methods defined in subclasses of
 Params::Callback. Callbacks are triggered either for every call to the
 Params::CallbackRequest request() method, or by specially named keys in the
 parameters to request().
 .
 The idea behind this module is to provide a sort of plugin architecture for
 Perl templating systems. Callbacks are triggered by the contents of a request
 to the Perl templating server, before the templating system itself executes.
 This approach allows you to carry out logical processing of data submitted
 from a form, to affect the contents of the request parameters before they're
 passed to the templating system for processing, and even to redirect or abort
 the request before the templating system handles it.