Metadata - List of File Types/Field Sets?

I am currently trying to add a new Field Set for Web Documents that would include for example: .htm .html .xml .php .js .asp .just to name a few.

But I don't know what to put in the File Type box for example the Photos has img,raw and Documents has office,ooffice. 

Where do I get a list of these? img,raw,office,ooffice,wvideo,video?