In my previous post I don't think I was clear about the methodology that Avalon uses to hack (err, customize) the XAML parsing. This caused Pete Cole to observe:

"That a hack is 'by design' doesn't make it any less of an inelegant, unsatisfactory hack. This does explain some of the bizarre syntax I have previously complained about. One wonders if the implementation of XAML is becoming like writing Word Processors - you end up putting in kludges/hacks in the code to cope with particular strange cases. That's OK a) the hack works and b) its invisible to the 'user' (they just see the programming formatting correctly as they expect) - hacking implementation of a 'programming' language ain't going to work." [Pete Cole]

The interesting to note, it is actually the Style object that implements the custom parsing and serialization of markup to support the "as use" syntax. This interface is documented and discoverable (both by tools and developers). In addition any component can implement the interface and customize their parsing.

Hack, maybe. Invisible, no.