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.

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.