code: public function handleContainerElement(ContainerElement $element)
      {
          $this->result .= $this->indent() . $this->renderer->formatStartTag($element);
          if ($this->isIndentMode) {
              if ($this->breakControl->breaks($element)) {
                  $this->result .= $this->indent->stepUp();
                  $this->result .= $this->formatChildNodes($element);
                  $this->result .= $this->breakCode();
                  $this->result .= $this->indent->stepDown();
              } else {
                  $this->isIndentMode = false;
                  $this->formatChildNodes($element);
                  $this->isIndentMode = true;
              }
          } else {
             $this->formatChildNodes($element);
          }
          $this->result .= $this->renderer->formatEndTag($element);
      }
docs: ContainerElement を読み込みます.
  @param ContainerElement $element
  @see Context::handleContainerElement()