The LaTeX3 source contains a folder xor which contains, among other things, xo-grid, which is supposed to provide LaTeX3 with grid support. To quote Joseph Wright,
Getting to grips with
xoris one of the biggest challenges facing the LaTeX3 Project: the code is complex and has evolved over many years. As such, there is currently no good estimate of when it will be production ready. It's also worth noting that the code will almost certainly break any LaTeX2e package that relies on the LaTeX2e output routine.
However, I was unable to find good documentation about what exactly xoris. I suspect that the or might stand for "output routine", but that does not help much. What exactly is xor?
xorimplementation is not meant for production code so far (i.e. usage in documents) – May 23 '15 at 09:22orhttp://tex.stackexchange.com/questions/8212/an-explanation-of-latexs-output-routine andxis the typical way to mention a difference or a new feature such as package namesgraphicx,xparse,xstringand so on. – percusse May 23 '15 at 09:25xorin his 2000 paper: http://latex-project.org/papers/xo-pfloat.pdf . I believe the code has changed substantially since then (updated for expl3), but otherwise the ideas are still relevant. – Will Robertson May 28 '15 at 06:22