What is the class keyword before a function argument?

Why does this code work? See the class keyword in front on the f function argument? What does it change if I add it?

struct A
{
    int i;
};

void f(class A pA) // why 'class' here?
{
    cout << pA.i << endl;
}

int main() 
{
    A obj{7};
    f(obj);
    return 0;
}