This is a reimplementation of the front end of Google Search, wherein values are passed into URL parameters based on which Search feature is being used.
There are four seperate functionalities within the pages: Google Search, Google Image Search, Google Advanced Search, and the I'm Feeling Lucky button. The Advanced and I'm Feeling Lucky features are more complicated, though. The Advanced Search specifies parameters that the user wants to be omited, possibly included, and definitely included. The I'm Feeling Lucky feature redirects the user to the first result on the search page for which their initial query returned.
Check out this video to see how it works!