"edge of reference area"?

Section 4.2.2 of the Recommendation, paragraph 6, states:

Each area has the traits top-position, bottom-position, left-position, 
and right-position which represent the distance from the edges of its 
content-rectangle to the like-named edges of the nearest ancestor 
reference-area.

I'm confused by the application of the term "edge" to "reference-area". 
  As I'm given to understand, areas have rectangles (content, padding, 
border), while rectangles have edges.

Should the spec read, "...to the like-named edges of the 
content-rectangle of the nearest ancestor reference-area"?

I'm really struggling to learn XSL-FO, with Dave Pawson's book in one 
hand and the spec in the oth.... uh, in a window.  The book has been 
helpful, but for some reason or another it isn't quite doing it for me. 
  Can anyone suggest any other resources that I might try?

Slightly off-topic :-)... I've been reading Umberto Eco's "Foucault's 
Pendulum", and apropos of all these edges in XSL-FO, I particularly 
noticed the chapter header for Chapter 37:

	Whoever reflects on four things, it were better he had never been
	born: that which is above, that which is below, that which is before,
	and that which is after.
		-- Talmud, Hagigah 2.1


----
Mark Lundquist