[luatex] void box

[Robin Fairbairns]

Paul Isambert <zappathustra at free.fr> wrote:

> Andreas Matthias <andreas.matthias at gmail.com> a écrit:
> > 
> > What is the lua equivalent of a void box? I.e. how to
> > create a void box in lua?
> 
> I'm not sure that it can be done, strictly speaking. By a void box, I
> suppose you mean an unassigned box register (i.e. \voidb at x); now that
> I think of it, it is strange that \unhbox\voidb at x is allowed in the
> first place (if nothing is assigned to the register, how can you unhbox
> it?).

what do you mean by "unassigned"?

of course, without macros of some sort, \voidb at x won't be assigned
(i.e., the name won't mean anything).  i've not looked at context, but
both plain and latex execute \newbox \voidb at x, but in both cases they
only ever use it -- so nothing has been put into the virgin box.

does luatex not actually allocate a register until its first use?  if
not, it will have to allocate \voidb at x pretty often, in two of the "big
three" formats i know of.

robin
the un-knowledgeable