Credit Card Data within Form Validation

[eluser]brightdevice[/eluser]
To be more specific when using:

Code:

set_value('cc_number');

in the view

and

Code:

$this->form_validation->set_rules('cc_number', 'example', 'required');

in the controller

How is the cc_number being processed and then re-populated when there is an error detected within the form validation process?