Document exit codes

[phil294]

It would be great to somehow know which error code indicates which kind of failure. As in
1 = pid does not exist
2 = permission denied
3 = syntax / option parsing error
The above are dummy values. I just got exit code 2 and I have no idea what it means.
Invalid parameters like cpulimit abc should also finish with a non-zero code, which they dont.
Regards,

edit. it seems that error code 2 occurs when the executable has finished and ALSO when there was no process found at all. However, it always results in 0 if used together with -b. Is this really intended?