[R] S3 vs S4 class

[Terry Therneau]

  A simple example:
  	temp <- as.Date('2001-10-5')
  	class(temp)
  	  "Date"

How do I tell if "Date" is implemented as an S3 or an S4 class type?
I tried ?class, but didn't see anything obvious.  Functions like inherit() work
equally well with both types (which is a good thing).

  I expect the answer will be obvious - once someone points it out to me.

	Terry T