if the return IS a param, then it's also got to be marked dirty inside the method clears up some false positives
if the return IS a param, then it's also got to be marked dirty inside the method
clears up some false positives

the pattern, here, is someone passes a StringBuilder into a function that appends stuff to it and passes the same string builder back out.
in this case, we can assume it's clean going into the function, since the calling code would have gotten an error if it weren't.

DrShaffopolis/FxCop