What C++11 features does cereal use? [on hold]

cereal is a C++11 only library for serializing data. It only works with C++11, which got me wondering: what C++11 features does it use?

(A more subjective version of this question is—mod alert!—What C++11 features enabled the authors of cereal to write the library, e.g. what features were essential? Could you make a version of cereal without C++11 and how terrible would it be?)