Ask HN: How do you think this site works?

For those who haven't read the short story The Library of Babel by Borges, it's about a fictional universe consisting of an infinite library filled by books which contain every possible combination of letters from the English alphabet.

In the story, people wander the vast Library for all their lives, seeking books which hold anything recognizable. Statistically, the odds of finding a book with even one intelligible sentence is next to nothing. But in theory, if every story is written there, then somewhere is a book which predicts your whole life, and another which tells correctly the location of any book you might seek, and so on.

This website reproduces that fictional universe in digital form. But if you look at the About page, it explicitly says that they do not simply generate and store each page as it's requested.

So how could this work? Click "Browse" to enter the library, or "Search" to find any text you can imagine somewhere in the library. The "Search" function confounds me more than any other aspect of this. Try a lengthy sentence describing you, even use your own name, and it's there, of course.....but how can it find it so fast?

https://libraryofbabel.info/