/// Provides the behavior for the "measure" pass of Silverlight layout. Classes can override this method to define their own measure pass behavior.
/// <param name="availableSize">The available size that this element can give to child elements. Infinity can be specified as a value to indicate that the element will size to whatever content is available.</param>
/// The size that this element determines it needs during layout, based on its calculations of child element sizes.
As you correctly noticed these panels are almost the same. The reason why we have created a panel that is almost the same as the standard WPF one, is that we wanted to provide all controls we have for Silverlight and we needed to create such a panel for Silverlight, because there is no standard one there. If you are going to build a WPF application (if you are not planning to port it to Silverlight), I would advise you to use the WPF DockPanel. If you are going to port the application to Silverlight, my advise is to use the RadDockPanel, because there is one in the RadControls for Silverlight as well and this will easy porting of the code and XAML.
Hope this answers your question.
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