I am working with System->user->Add new user->User Role.  

I am changing in core file for temporary purpose.  

**Expected Result:**  

Want to apply class 'validate-one-required-by-name' to user role radio button.  

**What I Done:-**  

> 
> magento\app\code\core\Mage\Adminhtml\Block\Permissions\User\Edit\Tab\Roles.php
> 
> 
> 

I have added class to radio button. as below. But it is not reflecting on webpage.

```
protected function _prepareColumns()
{

    $this->addColumn('assigned_user_role', array(
        'header_css_class' => 'a-center',
        'header'    => Mage::helper('adminhtml')->__('Assigned'),
        'type'      => 'radio',
        'class'     => 'validate-one-required-by-name',
        'html_name' => 'roles[]',
        'values'    => $this->_getSelectedRoles(),
        'align'     => 'center',
        'index'     => 'role_id'
    ));

```

Current Outout is  

> 
> input type="radio" class="radio" value="1" name="roles[]"
> 
> 
> 

Required

> 
> input type="radio" class="radio validate-one-required-by-name" value="1" name="roles[]"
> 
> 
> 

Thanks in advance.