/**
 * Form build callback of {step} step.
 *
 * @param array $form_state
 *   Drupal form_state array.
 * @param mixed $next_step
 *   Step name that is to follow.
 * @param mixed $params
 *   Additional params passed into form steps.
 *
 * @return array
 *   Drupal form array.
 */
function {step}(&$form_state, &$next_step, $params) {
  $next_step = {next_step};

  $form = array();

  $form['step_info'] = array(
    '#type' => 'markup',
    '#markup' => '{step}'
  );

  return $form;
}