views_element_validate_tags

views_element_validate_tags($element, FormStateInterface $form_state)

function views_element_validate_tags($element, FormStateInterface $form_state) {
  $values = array_map('trim', explode(',', $element['#value']));
  foreach ($values as $value) {
    if (preg_match("/[^a-z_]/", $value)) {
      $form_state->setError($element, t('The query tags may only contain lower-case alphabetical characters and underscores.'));
      return;
    }
  }
}