Legal to overwrite std::string's null terminator?

Question

In C++11, we know that std::string is guaranteed to be both contiguous and null-terminated (or more pedantically, terminated by charT(), which in t

Answer 1

LWG 2475 made this valid by editing the specification of operator[](size()) (inserted text in bold):

Otherwise, returns a reference to an object of type charT with value charT(), where modifying the object to any value other than charT() leads to undefined behavior.