Some of the fields such as [WikiArtistSearchURL] and [Search] are built-into MC. [Search] will be based on the currently selected item, and this would vary for different media types.
You can combine various fields and construct a query that uses other fields too. Examples:
http:////images.google.com//images?q=Hexify([Artist]) Hexify([Album])
http:////www.youtube.com//results?search_query="Hexify(regex([Artist] [Name], /#^(.+?)(?: [[(]extended\b[^)\]]*[)\]])?$#/, 1))"&btn=&type=all
http:////www.allrovi.com//search//movies//Replace([Name], ,+)