Why does it go to all this trouble to find when to use a BRIN index without even expanding on the name of it?

"Chapter 71. BRIN Indexes"[0]

> BRIN stands for Block Range Index. BRIN is designed for handling very large tables in which certain columns have some natural correlation with their physical location within the table.

[0] https://www.postgresql.org/docs/current/brin-intro.html