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/**
 * Adds subscript and superscript buttons for Wordpress's WYSIWYG
 * editor (disabled by Wordpress by default)
 *
 * @param $buttons
 * @return array
 */
function expose_mce_buttons_2($buttons) {

  $buttons[] = 'superscript';
  $buttons[] = 'subscript';

  return $buttons;

}
add_filter('mce_buttons_2', __NAMESPACE__ . '\\expose_mce_buttons_2');