You've probably figured out that Head Librarians can rename Great
Libraries. But it may not be clear that Head Librarians can also rename
annexes. Annexes are individual rooms. The main room with the catalog is
an annex in and of itself and can thus be renamed. New annexes cost 1
million gold, and there is no limit to how many annexes a city or
commune may purchase. Using the LIBRARY command in an annex will only
interact with books in that annex, which should help sorting books into
various categories or sections.

Penned by my hand on the 13th of Tzarin, in the year 127 CE.