Avalonia/tests/Avalonia.Generators.Tests/Views/AttachedProps.xml

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:custom="clr-namespace:Avalonia.ReactiveUI;assembly=Avalonia.ReactiveUI"
        xmlns:rxui="http://reactiveui.net"
        x:Class="Sample.App.AttachedProps"
        Design.Width="300">
    <TextBox Name="UserNameTextBox"
             Watermark="Username input"
             UseFloatingWatermark="True" />
</Window>