Definitions for "Viewable"
A window is ``viewable'' if it and all of its ancestors are mapped. This does not imply that any portion of the window is actually visible. Graphics requests can be performed on a window when it is not viewable, but output will not be retained unless the server is maintaining backing store.
Pertaining to a mapped window whose ancestors are all mapped; not necessarily visible. Graphics requests can be performed on a window when it is not viewable, but output will not be retained unless the server is maintaining backing store.
Keywords:  capable
capable of being viewed