If I understand it correctly, the "reference point" of a layout object
should be its relative (0,0) coordinate. It is possible to display
that point using a small function: [...]
It would be very nice if appendix A.8, "The Emmentaler font", could
display the metrics boxes as given in the proof output of METAFONT
(see image for an example; please ignore the point numbers, which are
of no relevance for the question at hand). Maybe a skilled Scheme
author could add this, also magnifying the Emmentaler glyphs a bit...