form_validation and Callbacks function

[eluser]Unknown[/eluser]
First, sorry for my English.
I need ue form_validation and calbacks function.

Code:

$this->form_validation->set_rules('tag', 'lang:tag_tag', 'min_length[3]|callback_testtags');

Problem, was check function I cannt use in controller. I use custom modular extension.
I think define check function in plugin or in helper. But this function was NOT called.
What can I use check function, was detine in helper?

[eluser]InsiteFX[/eluser]
Search form validation modular extensions

InsiteFX