Russ Cox explains how Google Code Search worked

After Google Code Search was retired, Russ Cox explains how it worked.
An essential part is using a q-gram index with q=3.

http://swtch.com/~rsc/regexp/regexp4.html

Perhaps I will, at some point, adjust my "Algorithms on Sequences" lecture to incorporate regular expression search again. I did this once in the past, but then removed the topic to have time for other, seemingly more important, topics in the lecture.