Codeigniter form checkbox group validation without using jquery or javascript

[eluser]Unknown[/eluser]
Just want to validate with codeigniter if at least one of the following checkbox fields is checked (without using jquery or javascript). Please help me

Code:

$data = array(
             'name'        => 'cat',
             'id'          => 'cat',
             'value'       => 'accept',
             'checked'     => FALSE,
             'style'       => 'margin:10px',
             );
             echo form_checkbox($data);
             echo form_label("Cat<br>","cat");

             $data = array(
             'name'        => 'dog',
             'id'          => 'dog',
             'value'       => 'accept',
             'checked'     => FALSE,
             'style'       => 'margin:10px',
             );
             echo form_checkbox($data);
             echo form_label("Dog<br>","dog");

             $data = array(
             'name'        => 'parrot',
             'id'          => 'parrot',
             'value'       => 'accept',
             'checked'     => FALSE,
             'style'       => 'margin:10px',
             );
             echo form_checkbox($data);
             echo form_label("Parrot<br>","parrot");

[eluser]CroNiX[/eluser]
http://ellislab.com/codeigniter/user-gui...ation.html