Can't understand C++11 template function parameter deduction

template <int T> struct int2type{};

template<int I>
void func( int2type<I> )
{
     printf("int_val: %i\n", I);
}

int main(int argc, char *argv[])
{
    func( int2type<10>() ); 
}

Of course it prints 10.

I have some basic idea of how templates and type deduction works, but i can't understand this code. What is the magic behind I? How we know I from int2type instance passed to func?