WPF: A Beginner's Guide - Part 4 of n

<Window x:Class="Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:Attached_Properties_DPs" 
    local:AttachedPropertyChildAdder.IsMasterHeaderApplied="true"
    WindowStartupLocation="CenterScreen" 
    Title="Attached_Properties_DPs" Height="400" Width="600">
    <!-- Extra content will be added here at runtime if the 
             local:AttachedPropertyChildAdder.IsMasterHeaderApplied="true" is set to true
             try changing the value of this in the top of this file, set it false and run me.
             See that there is no header applied if its false, and there is if its true -->
    <Button x:Name="btn1" Content="click me" Margin="10,10,10,10" Click="btn1_Click"/>
</Window>