public DesignTimeTextSelection(SceneElement textElement, IViewTextBox editingTextBox)
 {
     this.textElement = textElement;
     this.start       = editingTextBox.SelectionStart;
     this.end         = editingTextBox.SelectionStart + editingTextBox.SelectionLength;
     this.length      = editingTextBox.Text.Length;
 }
 protected TextBoxEditProxyBase(BaseFrameworkElement textSource)
     : base(textSource)
 {
     this.ProxyPlatform = textSource.DesignerContext.DesignerDefaultPlatformService.DefaultPlatform;
     this.textBox       = this.ProxyPlatform.ViewTextObjectFactory.CreateTextBox();
 }