What does it mean to write arguments to a function like function(num1[, ...[, numN]])?

Question

JavaScript

How to understand such a record?
Square brackets and commas at the beginning are confusing, I would like to know why they write it that way.

Answer 1

square brackets in help and examples indicate optional parameters.
that is
, it says that it can be both
function(1) and function(1,1,1,1,1)
And for example, a record like:
means that x, y are mandatory parameters, z is optional. Therefore, you can call both
function (1,2) and function(1,2,3), but not function(1,2,3,4)

Answer 2

An optional part is written in square brackets.