Avalon Architect Chris Anderson has an interesting post on XAML vs. Serialization on his blog Simplegeek

" XAML was designed to be a compromise markup format, that balanced the toolability and readability aspects of a markup. You can think of HTML as a markup that was squarely designed to be readable, but not very toolable. SOAP on the other hand is very toolable, but almost impossible to read. In the design of XAML we constantly walk the line between the two. XAML has support for inline code, customer parser extensions, and multiple representations of the same structure. "