In classical roff systems, there was a funny naming scheme for macro packages, due to a simplistic design in option parsing. Macro packages were always included by option when this option was directly followed by its argument without an intervening space, this looked like a long option preceded by a single minus — a sensation in the computer stone age. To make this optically working for macro package names, all classical macro packages choose a name that started with the letter which was omitted in the naming of the macro file.
For example, the macro package for the man pages was called man, while its macro file tmac.an. So it could be activated by the argument an to option or for short.
For similar reasons, macro packages that did not start with an had a leading added in the documentation and in talking; for example, the package corresponding to tmac.doc was called mdoc in the documentation, although a more suitable name would be doc. For, when omitting the space between the option and its argument, the command line option for activating this package reads
To cope with all situations, actual versions of groff(1) are smart about both naming schemes by providing two macro files for the inflicted macro packages; one with a leading the other one without it. So in groff, the man macro package may be specified as on of the following four methods:
Recent packages that do not start with do not use an additional in the documentation. For example, the www macro package may be specified only as one of the two methods:
Obviously, variants like -mmwww would not make much sense.
A second strange feature of classical troff was to name macro files according to In modern operating systems, the type of a file is specified as postfix, the file name extension. Again, groff copes with this situation by searching both anything.tmac and tmac.anything if only anything is specified.
The easiest way to find out which macro packages are available on a system is to check the man page groff(1), or the contents of the tmac directories.
In groff, most macro packages are described in man pages called groff_name(7), with a leading for the classical packages.