What does a window manager have to do to be GNOME-compliant

There are three big things:

• It must be fully ICCCM compliant, especially with proper X Session Management support.

• It must support MWM hints.

• It must support GNOME hints.

For more detailed information, see the GNOME Window Manager Compliance page at http://www.gnome.org/devel/gnomewm/book1.html