Drupal 7 form api. Add custom class to element after validation

Question

I looked around and could not find the solution as to how to add a custom class to the form element/elements or the <form> tag for that matter. I have a custom form validation function which does some custom validation. form_set_error does set an error class on the elements but I wanted to add my custom class anywhere within the form tag.

Answer 1

Since the goal is just to customize the display of your field on error, a cleaner way is to create your own theme_form_element() in your theme and use the function form_get_error($element) to add the class you want if any error is returned on a field. Using this method you can also display the error message next to the field in error, instead of on top of the form.

Answer 2

I found the answer here. Turns out you can use $form_state to make alterations to form after submission. I did

if($haserror) {
    $form_state['complete form']['#attributes'] = array('class'=>array('contains_error'));
}