[Last modified: July 96]

Answer: (See also the previous subject.) This is actually several related
questions with answers from David B. Lewis (d.lewis@opengroup.org) and Kenton
Lee (http://www.rahul.net/kenton/).

 1. Is it possible to run an X11R6 server with a Motif 1.2.* runtime
 environment (Motif libs and Motif Window Manager)?

David> Yes. The X11 protocol has not changed in its various versions, so
all X servers are compatible. There are differences, though, in
the fonts that are available and in a few of the gray areas in the
interpretation of the protocol. The fonts distributed by the X
Consortium form a standard set, though, and I know of no cases in
which changes in X11R6 cause problems for Motif programs (we are
using Motif with X11R6 servers here).

 2. Is there any possible conflict with Motif 1.2.* applications and an
 X11R6 server (assuming a Motif 1.2.* runtime environment)?

David> The only situation that I could imagine is a case in which Motif
1.2 code was written to depend on a particular bug or behavior of
an X11R5 server; I know of no such cases. Because of the stability
of the X11 protocol, Motif 1.2 programs should work with any
available X server, current and future.

 3. If Motif 2.0 is installed such that the Motif libraries and mwm are
 versions 2.0, is there 100% binary compatibility with statically linked
 Motif 1.2.* applications? If not, what are the known or potential problems?

David> There are additional support files in both the Motif and X11 areas
which are used at run-time. There are no known problems using Motif
1.2 *static* applications in a Motif 2.0 environment.

Kenton writes: R6 was designed to be backwards binary compatible with R5 and
most vendors have done a good job in implementing this.  Still, I wouldn't
recommend that my customers do this until I tested configurations similar to
theirs.

Motif 2.0 is backwards compatible with Motif 1.X in most cases.  I think Doug
Rand's comments in [the previous subject of the Motif FAQ] covers the
important issues.  In general, well written applications shouldn't have
problems, but some applications aren't well written.  Again, I would test
before making recommendations to my customers.

The above comments apply to run-time linking (shared library) compatibility.
If you statically link, the only problems I can imagine are the common ones
like installed fonts, supported server extensions, input methods, color name
databases, default visual types, etc.