Possible shapes are "RECT", "CIRCLE", and "POLYGON" which specify
rectangular, circular, and polygonal regions respectively...
...For a polygon the coordinates are specified as
"x1,y1,x2,y2,...,xn,yn" specifying the coordinates of successive
vertices of the polygon. If the last point is not the same as
the first point, the browser should infer a side connecting them.
Polygons must be simple, with the sides not crossing each other.
There is no restriction to the number of sides for a polygon
except for the number of points specifiable within the LITLEN of
the HTML DTD.
-- Jim Seidman, Senior Software Engineer, Spyglass Inc.