The window is mapped with XMapWindow
or related routines.
All its ancestors must be mapped. This
condition is always satisfied for the children of the root
window, the top-level windows of each application.
The window must not be obscured by visible
sibling windows or their
ancestors this depends on the stacking order. When first
mapped, a window appears on top of its siblings, which will
be on top of all windows if its parent is the root window.