Extra typename keyword in template parameter list: is it valid or not?

Question

The following code compiles successfully with clang 3.5.0 and g++ 4.9.0 (with -Wall -Wextra -pedantic-errors flags) under C++03 (flag -std=C++03), C++11 (flag -std=C++11), and C++14 (flag -std=C++14):

namespace N
{
    typedef int T;

    enum E{};
}

template <typename N::T>
struct ST{};

template <typename N::E>
struct SE{};

int main()
{
}

Is it valid to add extra typename keyword before a non-type template parameter declaration?

---

Note that the following code doesn't compile (as C++03, C++11, and C++14 code):

typedef int T;

enum E{};

template <typename T t>
struct ST{};

template <typename E e>
struct SE{};

int main()
{
}

But the following one compiles fine again (C++03, C++11, and C++14):

typedef int T;

enum E{};

template <typename ::T>
struct ST{};

template <typename ::E>
struct SE{};

int main()
{
}

Answer 1

It is allowed, but only with qualified names:

typename-specifier:
          typename nested-name-specifier identifier
          typename nested-name-specifier template_opt simple-template-id

So typename E is wrong according to the grammar. typename N::E is not since the name is qualified. The third case, typename ::E, is fine since :: is a valid nested-name-specifier.

The C++03 standard specifies in [temp.res]/5 that

The keyword typename shall be applied only to qualified names, but those names need not be dependent.

The C++11 standard states this nowhere explicitly but inside a note in [temp.names]/5:

[ Note: As is the case with the typename prefix, the template prefix is allowed in cases where it is not strictly necessary; i.e., when the nested-name-specifier or the expression on the left of the -> or . is not dependent on a template-parameter, or the use does not appear in the scope of a template. — end note ]

The same note exists in the exact same place in the C++14 standard.