Avalonia/samples/Sandbox/MainWindow.axaml

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
        x:Class="Sandbox.MainWindow">
  <StackPanel>
    <TextBox x:Name="txtBox" />
    <TextPresenter Text="Hello World" PreeditText="{Binding #txtBox.Text}" CaretIndex="11"/>
  </StackPanel>
 
</Window>