WindowContainer can be used to provide an area where a window-like control can be displayed. This is particularly useful in an XBAP application, where windows can't be popped up. ChildWindow or MessageBox controls can be added and constrained in a WindowContainer. When a child of the WindowContainer is modal (modal ChildWindow or MessageBox), the background color of the WindowContainer can be set. In WindowContainer, the modal windows (modal ChildWindow or MesssageBox) will always be in front, preventing the use of other windows from the WindowContainer.