Why does function c() accept an undocumented argument?

Question

The documentation for the base function c() shows its default arguments as

c(..., recursive = FALSE)

Now, if we define

<

Answer 1

c is an S4 Generic function, which means that a different function is called depending on its arguments.

Not all of those functions take the argument use.names, so it does not make sense for it to be documented in the documentation for c().

Answer 2

I think that it is due to the recursive=TRUE which I believe must use the same code as unlist. The use.names parameter is described in ?unlist.