"diff()" provides a basic set of services akin to the GNU "diff"
utility. It is not anywhere near as feature complete as GNU "diff", but
it is better integrated with Perl and available on all platforms. It is
often faster than shelling out to a system's "diff" executable for small
files, and generally slower on larger files.

Relies on Algorithm::Diff for, well, the algorithm. This may not produce
the same exact diff as a system's local "diff" executable, but it will
be a valid diff and comprehensible by "patch". We haven't seen any
differences between Algorithm::Diff's logic and GNU diff's, but we have
not examined them to make sure they are indeed identical.