>> It is probably not a bad idea to skim for some ideas... although
>> you probably have done so already.
>
> yes, but not very thoroughly back in 2000 and since then xor got to a
> sudden hold for private reasons. so it is certainly worthwise to redo
> that exercise

Yes, please. Something like xor with grid layout possibilities which
will work before LaTeX3 would be great.

Ulrich