The display of multiple Viewports on the screen normally depends on the
sequence with which they are made visible and hence the last viewport that
is made visible may occlude others. UIPACK contains a mechanism whereby each
Viewport may be assigned a Viewport Priority. A Viewport having a high priority
will occlude one having lower priority, irregardless of the sequence with which
they are displayed. Furthermore, a Viewport may be inhibited from being
displayed by adjustment of its priority (as an alternative to just ``hiding" it).
Note that UIPACK also contains a mechanism whereby any Viewport may become
the ``Top" one, irregardless of its Priority. This feature should be used with
caution since such an action will have unpredictable results when further
Viewports (having different priorities) are made visible.
Viewport Priorities may be defined to be any valid Integer, where Zero is the
Default Priority and negative priorities will disable the viewport from being
displayed.