<Window x:Class="Controls.LabelTest"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="LabelTest" Height="300" Width="300"
    >
  <StackPanel Margin="5">
    <Label Target="{Binding ElementName=txtA}">Choose _A</Label>
    <TextBox Name="txtA"></TextBox>
    <Label Target="{Binding ElementName=txtB}">Choose _B</Label>
    <TextBox Name="txtB"></TextBox>

  </StackPanel>
</Window>
