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5.19 Using Fonts
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In digital typography, a "font" is a collection of characters in a
specific typeface that a device can render as glyphs at a desired
size.(1)  (*note Using Fonts-Footnote-1::) A 'roff' formatter can change
typefaces at any point in the text.  The basic faces are a set of
"styles" combining upright and slanted shapes with normal and heavy
stroke weights: 'R', 'I', 'B', and 'BI'--these stand for roman, italic,
bold, and bold-italic.  For linguistic text, GNU 'troff' groups
typefaces into "families" containing each of these styles.(2)  (*note
Using Fonts-Footnote-2::) A "text font" is thus often a family combined
with a style, but it need not be: consider the 'ps' and 'pdf' devices'
'ZCMI' (Zapf Chancery Medium italic)--often, no other style of Zapf
Chancery Medium is provided.  On typesetting devices, at least one
"special font" is available, comprising "unstyled" glyphs for
mathematical operators and other purposes.

   Like AT&T 'troff', GNU 'troff' does not itself load or manipulate a
digital font file;(3) (*note Using Fonts-Footnote-3::) instead it works
with a "font description file" that characterizes it, including its
glyph repertoire and the "metrics" (dimensions) of each glyph.(4)
(*note Using Fonts-Footnote-4::) This information permits the formatter
to accurately place glyphs with respect to each other.  Before using a
font description, the formatter associates it with a "mounting
position", a place in an ordered list of available typefaces.  So that a
document need not be strongly coupled to a specific font family, in GNU
'troff' an output device can associate a style in the abstract sense
with a mounting position.  Thus the default family can be combined with
a style dynamically, producing a "resolved font name".

   Fonts often have trademarked names, and even Free Software fonts can
require renaming upon modification.  'groff' maintains a convention that
a device's serif font family is given the name 'T' ("Times"), its
sans-serif family 'H' ("Helvetica"), and its monospaced family 'C'
("Courier").  Historical inertia has driven 'groff''s font identifiers
to short uppercase abbreviations of font names, as with 'TR', 'TI',
'TB', 'TBI', and a special font 'S'.

   The default family used with abstract styles can be changed at any
time; initially, it is 'T'.  Typically, abstract styles are arranged in
the first four mounting positions in the order shown above.  The default
mounting position, and therefore style, is always '1' ('R').  By issuing
appropriate formatter instructions, you can override these defaults
before your document writes its first glyph.

   Terminal output devices cannot change font families and lack special
fonts.  They support style changes by overstriking, or by altering
ISO 6429/ECMA-48 "graphic renditions" (character cell attributes).

* Menu:

* Selecting Fonts::
* Font Families::
* Font Positions::
* Using Symbols::
* Character Classes::
* Special Fonts::
* Artificial Fonts::
* Ligatures and Kerning::
* Italic Corrections::
* Dummy Characters::