Add brackets around the spine subtitle

Error²Federal courts, Illinois courts21st and 22nd editions

A service's volume can be given as a subtitle from the volume's spine; brackets keep it from being read as the start of the title.¹

1. 1R. 19.1(a) Volume. Tables: R. 3.1(a) Volumes.
2. 2An error: the rule in note 1 allows one form, and this is not it.