Use of contains in S4 classes

setClass("B", representation=representation("B", extra="numeric))
setClass("B", representation=representation(extra="numeric"),
	contains="B")
Are these the same?  If not, how do they differ?

What about
setClass("B", representation=representation("B", extra="numeric"),
	contains="B")
?

As far as I can tell, the Green Book doesn't talk about a contains
argument to setClass.

Ross Boylan                                      wk:  (415) 502-4031
530 Parnassus Avenue (Library) rm 115-4          ross at biostat.ucsf.edu
Dept of Epidemiology and Biostatistics           fax: (415) 476-9856
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