Follow these links for information from HP's own Documentation:
Command Interpreter Access and Variables Programmer's Guide.
"Predefined Variables" (Appendix A in the MPE/iX Commands Reference Manual).
"Expression Evaluator Functions" (The first part of Appendix B - contains Table B-1).
"References and FINFO Specifications" (The middle part of Appendix B - contains Table B-2).
"Expression Evaluator Features" (The rest of Appendix B).
"A Detailed Look at CI Enhancements" by Jeff Vance of Hewlett Packard (from 5.5 Communicator).
"MPE/iX Release 5.5 Express 3 CI Enhancements" by by M. Gopalakrishnan (Gopi) and Jeff Vance of HP.
"MPE/iX Release 5.5
PowerPatch 5 CI Enhancements"
"5.5 MPEJXQ1 CI Enhancements" by Jeff Vance of Hewlett Packard.
"MPE/iX release 6.0 Express 1 CI enhancements"
"MPE/iX release 6.5 Express 3 CI enhancements"
"MPE/iX release 7.0 Express 1 CI enhancements"
Follow these links to other papers on UDCs and Command Files:
"MPE Programming" by Eugene Volokh of VESoft, presented at the 1983 (Montreal) HPIUG Conference.
(we've come a long way since 1983!)
"MPE/XL Programming" by Eugene Volokh of VESoft, presented at the 1988 (Orlando) Interex Conference.
"How to Write and Apply MPE XL Command Files" by Fred Ochs, Jr., printed in the September, 1991 Interact Magazine.
"A Beginner's Guide to UDCs and JCWs" by David L. Largent, presented at the 1988 (Orlando), 1989 (San Francisco), 1991 (San Diego), 1992 and (New Orleans) Interex Conferences (wow!). Also printed in the Interact Magazine in March, April, and May of 1989.
"101 (More or Less) Moral Things To Do With HPSusan..." by David L. Largent, presented at the 1993 (San Francisco) Interex Conference, and printed as "An Introduction to the MPE/iX Predefined Variables" in the May, 1994 Interact Magazine. (David has presented these two, and a few other papers at several Regional User's Group meetings, as well!)
"MPE Command File Tips and Techniques" Jack Bailie's PowerPoint tutorial, presented at the 1993 (San Francisco) Interex Conference, and "Command File Tips and Techniques" printed in the March, 1994 Interact Magazine.
"Programming the Command Interpreter" by Ken Robertson of Robelle, presented at the 1995 (Toronto) Interex Conference.
"All about User Defined Commands and Qedit Command Files" (Excerpted from Robelle's Qedit help file).
"UDCs and Command Files" from the HP3000 FAQ, Topic 6, Item 10.
Note #1: Any paper presented at an Interex Conference was published in the Proceedings for that year!