Add class to term-reference output
One option would be to preprocess the field:

function MYTHEME_preprocess_field(&amp;$vars) {
  if ($vars['element']['#field_name'] == 'field_tags') {
    array_walk($vars['items'], function(&amp;$el) { $el['#options']['attributes']['class'][] = 'some-class'; } );
  }
}