code: protected function openTag($tag)
      {
          $name = $tag->getTagName();
          if (! in_array($name, array_keys($this->tags))) {
              $this->tags[$name] = array();
          }
          $this->tags[$name][] = $tag;
      }
docs: Opens a tag for receiving content.
  Multiple tags will be receiving input at the same time.
  
  @param SimpleTag $tag        New content tag.