GNOME bug 119187 requests a new super-maximised window state where a window can be maximised across several Xinerama screens simultaneously, and a keybinding to toggle this state. Apparently you can do this in Windows XP by shift-clicking on the maximise button.
Since this is a new window state, it would require a change to the EWMH, which makes it nontrivial.
Would it be particularly useful to anyone out there?
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