form_set_error highlight single field in multiple value field

Question

Is it possible to highlight only one field with form_set_error when this field belongs to a multiple value field. Let's say I have a field name field_videos which accepts multiples values. After running validation, only video #2 isn't valid :

form_set_error('field_videos', t('Video URL not valid'));

How can I tell drupal to highlight only field #2 ?

Thanks

Answer 1

I solved this by using the delta of the field with the error. In this example, field_acceptable_domains is a multi-value text field and I'm using valid_url to validate each value.

// This is a multi-value field, so we need to loop through the values.
foreach ($form_state['values']['field_acceptable_domains'][LANGUAGE_NONE] as $delta => $url) {
  if (!valid_url($url['value']) && !empty($url['value'])) {
    form_set_error('field_acceptable_domains][' . LANGUAGE_NONE . '][' . $delta, t('The domain %domain is not valid.', array('%domain' => $url['value'])));
  }
}