It is meant to make the programmers work almost brainless but give them lots of flexibility.
License: LGPL v2 (see COPYING in the base of Elementary's source). This applies to all files in the source here.
Acknowledgements: There is a lot that goes into making a widget set, and they don't happen out of nothing. It's like trying to make everyone everywhere happy, regardless of age, gender, race or nationality - and that is really tough. So thanks to people and organisations behind this, aslisted in the Authors section above.