calling setGeneric() twice (don't; documentation comments)

I would expect setGeneric to create a new generic function and
nuke/mask 
methods associated with the generic that it replaces.

I tried a test in R 2.7.1, and that is the behavior.  I think it would
be worthwhile to document it in ?setGeneric.

Also, ?setGeneric advocates first defining a regular function (e.g.,
bar) and then doing a simple setGeneric("bar").  I think the advice for
package developers is different, so perhaps some changes there would be
a good idea too.

I thought I was defining setGeneric twice for a few functions, and thus
that it did work OK.  It turns out I have no duplicate definitions.

Here's the test:

setClass("A", representation(z="ANY"))

[1] "A"

setClass("B", representation(y="ANY"))

[1] "B"

setGeneric("foo", function(x) standardGeneric("foo"))

[1] "foo"

setMethod("foo", signature(x="A"), function(x) return("foo for A"))

[1] "foo"

a=new("A")
b=new("B")
foo(a)

[1] "foo for A"

foo(b)

Error in function (classes, fdef, mtable)  : 
  unable to find an inherited method for function "foo", for signature "B"

setGeneric("foo", function(x) standardGeneric("foo"))

[1] "foo"

setMethod("foo", signature(x="B"), function(x) return("foo for B"))

[1] "foo"

setGeneric("foo", function(x) standardGeneric("foo"))

[1] "foo"

setMethod("foo", signature(x="B"), function(x) return("foo for B"))

[1] "foo"

foo(a)

# here's where the disappearance of the prior setMethod shows
Error in function (classes, fdef, mtable)  : 
  unable to find an inherited method for function "foo", for signature "A"

foo(b)

[1] "foo for B"

So I guess I am going to pull the setGeneric's out.
Ross