comment form custom validation I am using a custom validation in my Drupal 7 comment form.I want to match the comment_body against a word "example" so if someone just type "example"in the comment body then it will show a error message that only the word "example" is not allowed. After reading drupal api documentation i codded like this:

function mango_form_comment_node_news_form_alter(&amp;$form, &amp;$form_state, $form_id){
    $form['comment_body']['#prefix'] = '&lt;div class="sm"&gt;Post your comment now!&lt;/div&gt;';
    $form['actions']['submit']['#value'] = 'Post Your Comment';
    $form['#validate'][] = 'banana';
}

function banana($form, &amp;$form_state) {
  if ($form_state['comment_body'] == "example") {
    form_set_error('comment_body', 'Your comment can not contain example!');
  }
}


Do not working :'( what i'm missing? Thanks
The values for comment_body is not stored in $form_state but in something like:

$form_state['values']['comment_body']['und'][0]['value']

function banana($form, &amp;$form_state) {
  if ($form_state['values']['comment_body']['und'][0]['value'] == "example") {
    form_set_error('comment_body', 'Your comment can not contain example!');
  }
}