/**
  * print a search form
  * 
  * this is a shortcut to print a preset search form.
  * 
  * @param bool $print
  * @return null|string
  */
 public function search_form($print = true)
 {
     //    error_log(__METHOD__.' target: '.$this->shortcode_atts['target_instance'].' module: '.$this->module);
     $search_term = PDb_FormElement::get_value_title($this->list_query->current_filter('search_term'), $this->list_query->current_filter('search_field'));
     $output = array();
     $output[] = '<input name="operator" type="hidden" class="search-item" value="LIKE" />';
     $output[] = '<input id="participant_search_term" type="text" name="value" class="search-item" value="' . esc_attr($search_term) . '">';
     $output[] = $this->search_submit_buttons();
     if ($print) {
         echo $this->output_HTML($output);
     } else {
         return $this->output_HTML($output);
     }
 }