Most users of the roff
language employ a macro package to format
their documents. Successful macro packages ease the composition
process; their users need not master the full formatting language, nor
understand features like diversions, traps, and environments. This
chapter aims to familiarize you with basic concepts and mechanisms
common to many macro packages (like “displays”). If you prefer a
meticulous and comprehensive presentation of the language and its
formatter, peruse GNU troff
Reference instead.