A pane is a both a container and a containee area. It serves only
 as a geometry management device. A 
pane%
 cannot be hidden or disabled like a 
panel% object.
A pane% object has a degenerate placement strategy for
 managing its children: it places each child as if it was the only
 child of the panel.  The horizontal-pane% and
 vertical-pane% classes provide useful geometry management
 for multiple children.
See also grow-box-spacer-pane%.
Changed in version 1.3 of package gui-lib: Changed the placement strategy to
stretch and align children, instead of
placing all children at the top-left
corner.
For information about the 
horiz-margin and 
vert-margin
    arguments, see 
subarea<%>. For information about the 
border, 
spacing, and 
alignment
    arguments, see 
area-container<%>. For information about the
    
min-width, 
min-height, 
stretchable-width, and
    
stretchable-height arguments, see 
area<%>.