How do I check geographic locations (for example, at careers.stackoverflow.com)?

Question

At http://careers.stackoverflow.com on the edit page

• http://careers.stackoverflow.com/cv/edit

- section Where do you want to work? - has a neat property that checks geographic locations and gives them some canonical name. For instance. I enter

Subotica

and it will end before

Zubotica, Severna Bachka, Serbia

Does it use any public API? Are there any open source possibilities for such a geocomplexor for further research? Are sanitation facilities provided by http://www.geonames.org/ ?