3.2.5 Save Under Flag
Some server implementations may preserve contents of
windows under other
This is not the same as preserving the contents of a window for you.
You may get better visual
appeal if transient windows (for example, pop-up menus) request that the system
preserve the screen contents under them,
so the temporarily obscured applications do not have to repaint.
You can set the save-under flag to
If save-under is
the X server is advised that, when this window is mapped,
saving the contents of windows it obscures would be beneficial.
Christophe Tronche, email@example.com