There are several changes in Ada 2012, among them there is the introduction of Contract Programming, and one of its sub-features is the Old (prestate):

http://www.ada-auth.org/cgi-bin/cvsweb.cgi/ai05s/ai05-0145-2.txt?rev=1.8

A general short introduction to the differences of Ada 2012: http://www2.adacore.com/wp-content/uploads/2006/03/Ada2012_Rational_Introducion.pdf

Bye,
bearophile