http://www.cnblogs.com/idior/archive/2010/06/04/1751738.html
The secret is behind a property called LogicalChildren. Panel, ItemsControl, ContentControl, and Decorator, which are the most common base classes, all define this property make the logical tree operate already.
LogicalChildren是用来实现以下列出的功能的，定义在基类FrameworkElement之上,而原文的列表里的Items,Children，Content之类的的属性是各个类自己维护的属性。LogicalChildren是以下关键能力实现的基础：
继承DependencyProperty（wpf的重要而容易被忽略的特性就是dp可以从树上的父元素获得）
DynamicResource的寻找
对名字的支持（NameScope传递)
RoutedEvent的发生和传导