code: function handleInsert(node, newNode, refChild){
      return newNode != null
        ? node.insertBefore(isNode(newNode) ? newNode : createText(newNode), refChild || null)
        : null;
    }
docs: Insert newNode into node. If newNode is instance of Node, it insert without change; otherwise it converts to TextNode.
  @param {Node} node Target node
  @param {Node|*} newNode Inserting node or object.
  @param {Node=} refChild Child of node.
  @return {Node}