_appendUndo(target, selector, ...args) {
    this._undos.push({
      target: target,
      selector: selector,
      args: args
    });
  }
Appends an undo action to the internal stack.

@param {Object} target call `selector` on this object
@param {string} selector the method name to call on `target`
@param {...Object} args arguments to pass when calling `selector` on `target`
@private