title: Why is the return type of std::reverse_iterator::operator[] unspecified?
body: <p>I was wondering, why, in C++, the return type of <a href="http://en.cppreference.com/w/cpp/iterator/reverse_iterator/operator_at" rel="nofollow"><code>std::reverse_iterator::operator[]</code></a> is left unspecified. Shouldn't it be <code>std::reverse_iterator::reference</code>?</p>