handleOk_(e) {
    // First restore the selection so we can manipulate the field's content
    // according to what was selected.
    this.restoreOriginalSelection();

    // Notify listeners that the field's contents are about to change.
    this.getFieldObject().dispatchBeforeChange();

    // Now we can clear out what was previously selected (if anything).
    const range = this.getFieldObject().getRange();
    range.removeContents();
    // And replace it with a span containing our hello world message.
    let createdNode = this.getFieldDomHelper().createDom(
        goog.dom.TagName.SPAN, null, e.message);
    createdNode = range.insertNode(createdNode, false);
    // Place the cursor at the end of the new text node (false == to the right).
    goog.editor.range.placeCursorNextTo(createdNode, false);

    // Notify listeners that the field's selection has changed.
    this.getFieldObject().dispatchSelectionChangeEvent();
    // Notify listeners that the field's contents have changed.
    this.getFieldObject().dispatchChange();
  }
Handles the OK event from the dialog by inserting the hello world message
into the field.
@param {goog.demos.editor.HelloWorldDialog.OkEvent} e OK event object.
@private