What does ...=... do in R?

Question

What does ... = ... mean as a function parameter? I saw this in some R source code. I understand that ... is additional arguments, but not sure what the equals does?

Answer 1

It is superfluous and the same as .... Probably the author meant that the ... of the called function should equal to the ... of the calling function, but that's the same as using just ... (in fact the ...=... construct may be confusing since it may invoke the idea that arguments other than ... of the called function won't be used which is not true).