RE: Rectangles are not explained or cross-referenced in Elisp manual

[Drew Adams]

        The Elisp manual says nothing about rectangles. It mentions them in
        passing in a few places, with no explanation. Those places should at
        least contain a cross-reference to the Rectangles node of the Emacs
        manual.

    Rectangles are not a general Lisp facility; they are an internal data
    structure of one file.  We don't need to document them in the manual.

Agreed; we don't need to document them there. But, since we mention them, we
could usefully cross-reference the doc that explains what they are.