Thinking in C++(vol 1) Ch-12 Q-21

Got stuck here while going through Bruce Eckel TIC++

Create a class with an assignment operator that has a second argument, a string that has a default value that says “op= call.” Create a function that assigns an object of your class to another one and show that your assignment operator is called correctly.

Is this really possible. Does C++ allow operator=() to have multiple argument?? I tried this:

class X{
    public:
        X& operator=(const X& x,string val="op=call"){ //! error

        }
};

int main(){
    X x1;
    X x2;
    x2=x1;
}

Error given by compiler:

[Error] 'X& X::operator=(const X&, std::string)' must take exactly one argument

I think this is not a valid question or if it is then how to provide multiple argument to assignment operator??