# File lib/xml/dom2/document.rb, line 286
      def _checkNode(node)
        unless node.nodeType == ELEMENT_NODE ||
            node.nodeType == PROCESSING_INSTRUCTION_NODE ||
            node.nodeType == COMMENT_NODE ||
            node.nodeType == DOCUMENT_TYPE_NODE
          raise DOMException.new(DOMException::HIERARCHY_REQUEST_ERR)
        end

        if node.nodeType == ELEMENT_NODE
          @children.each do |n|
            if n.nodeType == ELEMENT_NODE
              raise DOMException.new(DOMException::HIERARCHY_REQUEST_ERR)
            end
          end
        end

        if node.nodeType == DOCUMENT_TYPE_NODE
          @children.each do |n|
            if n.nodeType == DOCUMENT_TYPE_NODE
              raise DOMException.new(DOMException::HIERARCHY_REQUEST_ERR)
            end
          end
        end
      end