We started these pages with four strings because we had never seen a comprehensive list anywhere. Nominally RFC 1945 and RFC 2068 define them (get RFCs) but only as an afterthought (the RFCs define HTTP 1.0 and 1.1). Browser IDs, more correctly User Agent IDs, appear, among other places, as the environmental variable HTTP_USER_AGENT in Apache. You need this information to make the fewest checks possible for the browser environment or how to optimise the display or ... to know who and what is crawling around your site. And if you want to check your browser string with our page or one from Julian Grammer will also give your IP address.