The best source of such information is in your R5/R6 sources in the file
ctlseqs.ms (R6: xc/doc/specs/xterm/ctlseqs.ms); a PostScript version is in
your R5 sources in mit/hardcopy/clients/ctlseqs.PS.Z and your R6 sources in
xc/doc/hardcopy/xterm/ctlseqs.PS.Z.

Both editions of O'Reilly's Volume 3, the X User's Guide, include an R5
version of the control sequences.

Other good sources of information include the R4 version of that document and
also the file in the R4 sources called mit/clients/xterm/ctlseq2.txt, a
compilation put together by Skip Montanaro (GE CR&D) listing the VT100
sequences. It dates from R3 but is fairly accurate.  A hardcopy version was
published in the December 1989 XNextEvent (the XUG newsletter).

In a pinch, a VT100 manual will do.

[last updated 10/91]