Hello,
BTW: Why is it possible to have 268435456 (2^28) catcode tables? That strikes me, more than 65536 registers, as nearly unlimited. Why not "only" 65536, especially since one would likely run out of memory long before exhausting this amount?
the same is true for the number of lua instances, one seldom needs more than a few, but we saw no reason for a limitation
That of course is true. Do you have any specific applications for catcode tables in mind?
[...] maybe in the long run a more sophisticated grouping model will surface, for instance we've been discussing assignments to registers that migrate after the the current group (handy for local calculations where the result has to be caried over) but this has a low priority (fonts, list manipulations has the highest)
I think this can be done in TeX right now (although it is a bit complicated). In <http://groups.google.com/group/comp.text.tex/browse_thread/thread/deb4f 30f546d7804/8954ab2efb7ab908>, a multi-token \aftergroup is described that could be used for this purpose. The \edef-based variation described in the second half would be a possible approach.
[...]
Jonathan