question regarding exit codes

Hello, 
I'd like to know what the exit codes are, and mean. I'm using the
force-output:yes option, and exit codes are sometimes 0,1,2...   
This conduct to some problems because I'm using tidy on msoffice generated
files that are not cleaned up without this option, and I must know if
everything worked fine to perform
other actions .
I'm using a java call to execute tidy, and the exit code is given by the
proc.getExitCode() method. Do you know if this exactly give the real 
exit code given by tidy or something guessed by java in function of the
state of the process?   
Thanks in advance.
 
Cyril Lavy.