/**
   * Handle payloads from an execute reply.
   *
   * #### Notes
   * Payloads are deprecated and there are no official interfaces for them in
   * the kernel type definitions.
   * See [Payloads (DEPRECATED)](https://jupyter-client.readthedocs.io/en/latest/messaging.html#payloads-deprecated).
   */
  function handlePayload(content: KernelMessage.IExecuteOkReply, parent: Notebook, child: BaseCellWidget) {
    let setNextInput = content.payload.filter(i => {
      return (i as any).source === 'set_next_input';
    })[0];

    if (!setNextInput) {
      return;
    }

    let text = (setNextInput as any).text;
    let replace = (setNextInput as any).replace;

    if (replace) {
      child.model.value.text = text;
      return;
    }

    // Create a new code cell and add as the next cell.
    let cell = parent.model.contentFactory.createCodeCell({});
    cell.value.text = text;
    let cells = parent.model.cells;
    let i = indexOf(cells, child.model);
    if (i === -1) {
      cells.pushBack(cell);
    } else {
      cells.insert(i + 1, cell);
    }
  }

 /**
  * Remove the first occurrence of a specific item from the list.
  *
  * @param item - The item to remove from the list.
  *
  * @return The index occupied by the item, or `-1` if the item is
  *   not contained in the list.
  */
 remove(item: T): number {
   let i = indexOf(this.internal, item);
   if (i !== -1) {
     this.removeItem(i);
   }
   return i;
 }

 it('should be reset when loading from disk', () => {
   let model = new NotebookModel();
   let cell = model.factory.createCodeCell();
   model.cells.pushBack(cell);
   model.fromJSON(DEFAULT_CONTENT);
   expect(indexOf(model.cells, cell)).to.be(-1);
   expect(model.cells.length).to.be(6);
 });

 /**
  * Get the index of the first occurence of an item in the list.
  *
  * @param item - The item of interest.
  *
  * @returns The index of the specified item or `-1` if the item is
  *   not contained in the list.
  */
 indexOf(item: T): number {
   return indexOf(this.internal, item);
 }

 /**
  * Test whether the list contains a specific item.
  *
  * @param item - The item of interest.
  *
  * @returns `true` if the list contains the item, `false` otherwise.
  */
 contains(item: T): boolean {
   return indexOf(this.internal, item) !== -1;
 }