5.19.3 Font Mounting Positions

To support typeface indirection through abstract styles, and for compatibility with AT&T troff, the formatter maintains a list of positions at which fonts required by a document are mounted. An output device’s description file DESC typically configures a set of pre-mounted fonts.¹⁷⁸ A font need not be explicitly mounted before it is selected; GNU troff searches GROFF_FONT_PATH for a file name matching the identifier and mount it on demand.

Request: .fp pos id [font-description-file-name]

Register: \n[.f]

Register: \n[.fp]

Mount a font under the name id at mounting position pos, a non-negative integer. When the formatter starts up, it reads the output device’s description to mount an initial set of faces, and selects font position 1. Position 0 is unused by default. Unless the font-description-file-name argument is given, id should be the name of a font description file stored in a directory corresponding to the selected output device. GNU troff does not traverse directories to locate the font description file.

The optional third argument enables font names to be aliased, which can be necessary in compatibility mode¹⁷⁹ since AT&T troff syntax affords no means of identifying fonts with names longer than two characters, like ‘TBI’ or ‘ZCMI’, in a font selection escape sequence. You can also alias fonts on mounting for convenience or abstraction. (See below regarding the .fp register.)

.fp \n[.fp] SC ZCMI
Send a \f(SChand-written\fP thank-you note.
.fp \n[.fp] Emph TI
.fp \n[.fp] Strong TB
Are \f[Emph]these names\f[] \f[Strong]comfortable\f[]?

‘DESC’, ‘P’, and non-negative integers are not usable as font identifiers.

Obtain a report of occupied font mounting positions (whether configured by the ‘DESC’ file, the fp request, or automatic mounting) on the standard error stream with the pfp request.¹⁸⁰

The position of the currently selected font (or abstract style) is available in the read-only register ‘.f’.

Copy the value of .f to another register to save it for later use.

.nr sF \n(.f
… text involving many font changes …
.ft \n(sF

The index of the next (non-zero) free font mounting position is available in the read-only register ‘.fp’. When using the ft request or \f escape sequence to select a font by name that is not listed in the device’s DESC file, GNU troff automatically mounts it at position ‘\n[.fp]’. If you mount a font at a position explicitly with the fp request, you should follow the same practice, though the program does not strictly enforce adherence.¹⁸¹