[R] Two ways to inherit in S4?

[Ross Boylan]

I'm puzzled that it seems possible to specify inheritance via the
"representation" and "contains" arguments to setClass.  The examples
that I've seen all seem to use contains only.

Is there some subtle distinction between these two approaches?
Originally I thought one had to repeat the same information in both
places, but that seems not to be the case.

Sorry about all these questions.
Ross