support for substitution groups, support for redefines?

	
Hi
Does anyone have a good overview of how well substitution groups and
redefines are supported in various processors. The last big project where I
used redefines extensively about half a year ago I had to redo halfway
through after running into too many problems, problems where the redefine
was proper and was supported by some processors but failed in others, even
more insidious where cases where I had redefined incorrectly and it
functioned in some processors or in some test instances only to fail later.
This has put me off redefines, now I'm on something where redefines and
substitution groups are being proposed as the extensibility mechanism. I've
had misgivings about substitution groups, finding them somewhat overly
complicated and have thus avoided them. How is their support?

Cheers
Bryan Rasmussen