execCommandInternal(command) {
    const domHelper = this.getFieldObject().getEditableDomHelper();
    const range = this.getFieldObject().getRange();
    range.removeContents();
    const newNode =
        domHelper.createDom(goog.dom.TagName.SPAN, null, 'Hello World!');
    range.insertNode(newNode, false);
  }
Executes a command. Does not fire any BEFORECHANGE, CHANGE, or
SELECTIONCHANGE events (these are handled by the super class implementation
of `execCommand`.
@param {string} command Command to execute.
@override
@protected