/// <summary>Also adds logic to find a control by name.</summary>
 /// <param name="key"></param>
 /// <returns></returns>
 protected override object OnIndex(object key)
 => base.OnIndex(key) ?? WpfPaneHelper.GetXamlElement(Control, key);                 // todo: XamlParser could do this.
 /// <summary></summary>
 /// <param name="key"></param>
 /// <returns></returns>
 protected override object OnIndex(object key)
 => base.OnIndex(key) ?? WpfPaneHelper.GetXamlElement(Control, key);