Unix in a Nutshell, Fourth Edition

The Solaris man macros use a number of macro, string, and number register names that begin with ], }, and ). Such names should be avoided in your own files.

The number registers D, IN, LL, P, X, d, m, and x are used internally by the Solaris man macros. Using .nr D 1 before calling the .TH macro generates pages with different even and odd footers.^[*]

^[*] This information was gleaned by examining the actual macros. It is not documented, so Your Mileage May Vary.