Whatever you type in is searched for in a large index file containing keywords and phrases descriptive of particular URLs. For example, if you search on 'mailer,' you will get URLs for all the mailers I know of. If you type 'text-based mailer,' you get Pine, Mutt etc. If you type 'mailer text-based,' you get nothing. Regular expressions acceptable to Perl should work here.
Some nonalphabetic characters have to be escaped.
Case is not significant.