Adding template specialization in std namespace

Question

Background:
I tried to answer the question Why isn't my overloading < operator not working for STL sort. One of my suggestion (apart from using predicate) was to move the custom operator < for std::string in namespace std so that it can be preferred by the compiler over templated version.

At lightening speed the answer was down-voted with following comment from a highly reputed user:

This is undefined behaviour, you are not allowed to add declarations to namespace std because it can change the behaviour of the standard library componens

My Question:
Is it okay to add template specialization for stl types even if the declaration of this specialization doesn't contain user defined data type?

---

^{p.s. I have deleted my answer as I am afraid it may be possibly wrong}

Answer 1

C++11, [namespace.std]§1:

The behavior of a C++ program is undefined if it adds declarations or definitions to namespace std or to a namespace within namespace std unless otherwise specified. A program may add a template specialization for any standard library template to namespace std only if the declaration depends on a user-defined type and the specialization meets the standard library requirements for the original template and is not explicitly prohibited.

The above paragraph explcitily prohibits specialisations which do not depend on a user-defined type.

As to the motivation: you wouldn't be adding a template specialisation, but a separate declaration, which is also prohibited.

Answer 2

Angew got the relevant quote, but the interpretation is flawed.

You propose to add a template specialization in namespace std. This is permitted only if it depends on a user-defined type. You specifically mention that it does not. Therefore, the preconditions for the exception are not met, and the basic rule (no additions) applies. Not OK.