I believe that the C++11 Standard, section 23.3.6, does not specify that vector const_reference back() const is a constexpr, so I believe the documentation here is in error.
- Yes, that's correct. constexpr has been added only in C++14 version of the standard. FYI there was a note explaining this, but it was buried in the text so it was easy to miss it. I've fixed this, thanks for reporting. P12 04:57, 1 July 2013 (PDT)