A size object
represents the size<-width and size<-height
of a (rectangular) area. Sizes are often used to communicate about sizes
with graphical
objects. Most graphical
objects interpret sizes in pixel units. Some textual graphical
object interpret them in character units.
Both the size<-width and the size<-height
of a size may be negative. See class area
for details on using negative width/height.
<-width and size<-height
of both size objects
are equal.<-width and height to size<-height.