5.8 Registers

In the roff language, numbers and measurements can be stored in registers. Many built-in registers exist, supplying anything from components of the date to details of formatting parameters; some of these are read-only. You can also define your own. Recall Identifiers, regarding the construction of valid names for registers. The register name space is separate from that used for requests, macros, strings, and diversions.

Each register (except read-only ones) can be assigned a format, causing its value to interpolate with leading zeroes, in Roman numerals, or alphabetically. Some read-only registers are string-valued, meaning that they interpolate text and lack a format.