Guide to LaTeX (4th Edition) (Tools and Techniques

378 Appendix A. The New Font Selection Scheme (NFSS)
subf * is like the empty function, but issues a warning that an explicit
substitute font has been loaded;
fixed * loads the specified font at its normal size, ignoring the size part;
if an optional argument is given, it is the point size to which the font
is scaled, as in
fixed * [11] cmr12 which loads cmr12 at 11 pt when
10 pt is requested.
All the above functions may be preceded by an s to suppress messages
to the monitor. Thus silent sub * is ssub *, and silent empty is s *.
As another example, consider the definition of bold, italic, typewriter,
for which there is no font in the Computer Modern collection:
\DeclareFontShape{OT1}{cmtt}{bx}{it}{
ssub * cmtt/m/it }{}
This substitutes (silently) for all sizes () the medium italic typewriter
attributes. Which fonts those are is determined by a \DeclareFontShape
command with those attributes.
The font definition commands may be issued in a package file, or even
in the document itself. However, the normal procedure is to store each of
the \DeclareFontEncoding commands in a file named codeenc.def (for
example, ot1enc.def for the OT1 encoding), and to place the commands
\DeclareFontFamily and \DeclareFontShape in a file whose name
consists of the encoding and family designations plus the extension.fd.
For example, the shape specifications for encoding OT1 and family cmr are
to be found in ot1cmr.fd. When a coding and family combination that is
not already defined is selected, LAT EX tries to find the appropriate.fd file
for input. It is therefore not necessary to input such files explicitly, for
they are loaded automatically as required.
Package: However, it is important that the encoding be declared beforehand. If
fontenc it is not already known in the current format, \DeclareFontEncoding
must be issued, either explicitly, or by loading the codeenc.def file. One
way to do this is to invoke the standard package fontenc, as for example
\usepackage[OT2,T1]{fontenc}
where the desired codings are listed as options in square brackets, the
last of which is made current.
The normal user will never need to worry about such problems. However,
L AT E X programmers will find things considerably easier for them.
For example, to install PostScript fonts under NFSS is almost trivial. The
common PostScript fonts are already defined as separate families in .fd
files of their own; for example, ot1ptm.fd associates PostScript Times
fonts to a family named ptm. A package to activate these fonts is supplied
under the name times.sty containing essentially the lines