Add ToolTip text to a TextBox

   
     

<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      HorizontalAlignment="Center" VerticalAlignment="Center">

<TextBox Width="100" ToolTip="Type something here" />

</Page>