code: protected function setWidget($tag)
      {
          if (strtolower($tag->getAttribute('type')) === 'radio') {
              $this->addRadioButton($tag);
          } elseif (strtolower($tag->getAttribute('type')) === 'checkbox') {
              $this->addCheckbox($tag);
          } else {
              $this->widgets[] = $tag;
          }
      }
docs: Sets the widget into the form, grouping radio buttons if any.
  
  @param SimpleWidget $tag   Incoming form control.