Visibility, Stacking Order And Mapping

Typically, X does not restrict the size and location of windows except that:

• No portion of a window can be displayed beyond the bounds of its parent window.
• Child windows always lie on top of their parent window. Hence, whenever a window is visible, any descendants contained within the exposed region are also visible.
• If two sibling windows overlap, the window with the higher stacking order will obscure the portion of the other window which it overlaps. A window's stacking order can only be altered relative to its siblings. For example, in figure 5, sibling windows 1 and 2 overlap, but part of window 2 is obscured by window 1, because window 1 has a higher stacking order.

Finally, when a window is created by the server, it is not displayed on the screen until it and all its ancestors are mapped. However, this does not guarantee that the window will be visible; for instance it may be obscured by other windows.