I am aware that once a reference is bound to an object it cannot be changed.
Therefore making the reference itself const (unlike a reference to a const object) cannot have any practical meaning.

Nevertheless I am wondering whether it is valid, because of a discrepenacy between compilers.

The following code is accepted by MSVC (though with a warning), but rejected by GCC and clang:

int main()
{
    int a = 5;
    [[maybe_unused]] int& const ref1 = a; 
}

Live demo

Is MSVC right to accept it ?