XAML
WPF 4 introduces XAML 2009, an updated version of XAML
with a number of useful refinements. However, there’s a
significant shortcoming: currently, it’s possible to use
XAML 2009 only in loose XAML files. Although Visual Studio
supports both loose and compiled XAML (as you’ll learn in this chapter),
compiled XAML isthe standard. This information will prepare you
for future releases of WPF, because XAML 2009 is slated to
become the new standard—once Microsoft has time to rewrite, test,
and optimize WPF’s XAML compiler.