"http://nlp.stanford.edu/IR-book/" resolves to the same resource.
Then (in the simplest case) the responding webserver is configured to treat the two hostnames (and possibly others) as identical and serve the same files.
So I guess there is magic. CNAMEs and virtual hosts and HTTP1.1.
I don't say it's not interesting, it's step forward compared to other articles in my collection [1][2][3] about the same subject allows to dive easily into the metrics and heuristics used in IR.
[1] https://www.youtube.com/watch?v=gJwFHSeFg44
[2] http://aakashjapi.com/fuckin-search-engines-how-do-they-work...
Tom Mitchell's popular definition (from his book "Machine Learning"), which is is even quoted in the opening of the Wikipedia article on Machine Learning, comes to mind:
"A computer program is said to learn from experience E with respect to some class of tasks T and performance measure P, if its performance at tasks in T, as measured by P, improves with experience E" [1]
[1]: Mitchell, T. (1997). Machine Learning, McGraw Hill. ISBN 0-07-042807-7, p.2.
[2]: https://en.wikipedia.org/wiki/Machine_learning#Overview
But of course, it's an interesting topic. If you want to learn more, the first edition of the most widely used textbook is free:
http://www-nlp.stanford.edu/IR-book/