Hello,
Sorry for stupid question, but just downloaded  trial and can't find example.

My application document is unique and is an UserControl. So I need this UserControl to be the "Background" of the docking area:
For example If I float all Panes to another screen, my UserControl must take all the available space in the window (except tool and status bar, of course). If I dock panes in the dock area the must reduce the space available for my UserControl. 

Thanks
Regards
Stephane

PS: Sorry wrong forum, It's about WPF not Silverlight ...