... X11
It is possible to use psglobal in Xpage reversed document; place it just before the last figure in Xyour document. This is living dangerously, and you do so at your own risk.
... X22
See `Appendix J: PostScript File Structuring Conventions' in XThe PostScript Language Reference Manual
... X33
The value need not be numeric; it may be a string, array, or procedure, among other things.