[NTG-context] Automatic typesetting of catalogue entries

[Taco Hoekwater]

Piotr Kopszak wrote:
> That's superb! Certainly worth wikifying, maybe someone better versed
> in ConTeXt than me cared also to explain what's going on in here. 

The first definition simply puts two on a page, using a counter
to decide whether it is processing the top one or the bottom one,
and using half of the page for each of them.

The second definition also has two per page, but it uses the height
of the typeset text to scale the images instead of using a fixed
value based on the page dimension. It pdftex's positioning extensions
to do so (that is the source the \hpos and \MPy commands). It has to
disregard the actual size of the placed graphic to prevent it from
interfering, and that is the reason for \ht\scratchbox\strutheight
line (consider it a vertical version of \llap).

Cheers, Taco