The core implementations for the DateTime.pm and DateTime::Duration modules originally came from Date::ICal and Date::ICal::Duration, both of which were written by Rich Bowen <firstname.lastname@example.org> with help from the Reefknot team. Nowadays much of this code has been rewritten to the point that it is fundamentally original work. Parts of the API come from Time::Piece, by Matt Sergeant <email@example.com>, who had help from Jarkko Hietaniemi <firstname.lastname@example.org>. That API was originally created by Larry Wall. None of the code is shared. The DateTime::Locale functionality is based in part on the Date::Language modules that come with Graham Barr's <email@example.com> TimeDate module suite. The strftime method in this module also borrows heavily from Graham's implementation. The week number and week year algorithms were taken from Steffen Beyer's Date::Calc module, but rewritten in Perl from scratch. The code for handling nanoseconds and the code for leap seconds were both largely written by Flavio Soibelmann Glock, who also has contributed various other features and fixes. Many others have helped out with code, ideas, and bug reports. See the Changes file for details.