Elemental typesetting functions can be be challenging to use directly
with complex documents.  A macro facility specifies how certain
routine operations, such as starting paragraphs, or printing headers and
footers, should be performed in terms of those low-level instructions.
Macros can be specific to one document or collected together into a
macro package for use by many.  Several macro packages available;
the most widely used are provided with groff.  They are
man, mdoc, me, mm, mom, and
ms.