In the area element description, the calspair units are said to have
the following format: "x1,y1 x2,y2".
This is not consistent with the mediaobjectco example, where the
coords are formatted as "x y".
Does it mean that "x y" is equivalent to "x,y x,y", or is it an error?
Besides, do the "units" attribute is inherited to the included
elements? The inheritence mechanism (if any) should be explained in
the areaspec, areaset and area elements descriptions.