Form element validation handler for \Drupal\rest\Plugin\views\row\DataFieldRow::buildOptionsForm().
public function validateAliasName($element, &$form_state) {
if (preg_match('@[^A-Za-z0-9_-]+@', $element['#value'])) {
form_error($element, t('The machine-readable name must contain only letters, numbers, dashes and underscores.'));
}
}