What is the meaning of ellipses in a copy constructor?

Question

Consider the following program:

#include <iostream>
struct Test
{
    int a;
    Test() : a(3)
    { }
    Test(const Test& t...)
    {
        std::cout<<"Copy constructor called\n";
        a=t.a;
    }
    int get_a()
    {
        return a;
    }
    ~Test()
    {
        std::cout<<"Destructor is called\n";
    }
};
int main()
{
    Test t;
    Test* t1=new Test(t);
    std::cout<<t.get_a()<<'\n';
    std::cout<<t1->get_a()<<'\n';
    delete t1;
}

Closely observe the three dots in parameter of copy constructor I was really surprised when I tried this program. What is the use of it? What does it mean?

What the language specification says about this?

I know that three dots are used to represent variable length arguments in variadic functions like printf() and scanf() etc and also variadic macros introduced by C99. In C++, if I am not wrong, they are used in variadic templates.
Is this code well formed? Is this variadic copy constructor that can take any number of arguments?

It compiles & runs fine on g++ 4.8.1 & MSVS 2010.

Answer 1

The draft standard in section 8.3.5 [dcl.fct] says , ... is synonymous with ... unless ... is part of abstract-declarator (emphasis mine):

[...]If the parameter-declaration-clause terminates with an ellipsis or a function parameter pack (14.5.3), the number of arguments shall be equal to or greater than the number of parameters that do not have a default argument and are not function parameter packs. Where syntactically correct and where “...” is not part of an abstract-declarator, “, ...” is synonymous with “...”.[...]

So it is a variadic function and as far as I can tell without additional arguments this is also a valid copy constructor, from section 12.8 [class.copy]:

A non-template constructor for class X is a copy constructor if its first parameter is of type X&, const X&, volatile X& or const volatile X&, and either there are no other parameters or else all other parameters have default arguments (8.3.6).

and this note says that ellipses are not parameters:

void g(int = 0, ...); // OK, ellipsis is not a parameter so it can follow
                      // a parameter with a default argument

which is backed up by the normative text above which says:

If the parameter-declaration-clause terminates with an ellipsis[...]

Note, since it was asked an abstract-declarator is a declarator without an identifier.