In man diff
FILES are `FILE1 FILE2' or `DIR1 DIR2' or `DIR FILE...' or `FILE...
DIR'. If --from-file or --to-file is given, there are no restrictions
on FILE(s). If a FILE is `-', read standard input. Exit status is 0
if inputs are the same, 1 if different, 2 if trouble.Exit status deserves its own section, just like man cat... which, wait... doesn't even mention exit status. OK... at least all man pages should mention it or all just say it in Info.
