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

\renewcommand{\rmdefault}{ptm}
\renewcommand{\sfdefault}{phv}
\renewcommand{\ttdefault}{pcr}
\renewcommand{\bfdefault}{b}
A.3. Installing fonts with NFSS 379
This makes Times ptm the default Roman family, invoked with the command
\rmfamily, Helvetica phv the default sans serif family (called by
\sffamily), and Courier pcr the default typewriter family (activated by
\ttfamily). The default attribute for bold face is defined to be b instead
of the regular bx, since bold extended is not provided by these fonts.
Another two examples of the usefulness of NFSS are the Cyrillic fonts
of the University of Washington (Section 12.4.2) and the extended EC fonts
with the Cork encoding (Section G.4.3). Both of these may be activated
within a document simply by selecting another encoding, OT2 for Cyrillic,
T1 for the EC fonts. (These encodings must first be declared, for example
with the fontenc package as illustrated on the facing page.)
A.3.7 Encoding commands
In L AT E X, special characters and accents are addressed by means of commands,
! such as \O to print the Scandinavian letter Ø. The position of this character in
the font tables depends on the encoding (character 31 in OT1 and 216 in T1), so
that it is necessary to redefine all such symbol commands when the encoding is
altered. This is carried out with the help of certain encoding commands, which
normally appear in the codeenc.def file along with the \DeclareFontEncoding
command.
To define a command that functions differently in the various encodings,
\ProvideTextCommand{\cmd}{code}[narg][opt]{def }
\DeclareTextCommand{\cmd}{code}[narg][opt]{def }
are available and behave just like \providecommand and \newcommand except
\cmd has the definition def only when the encoding code is active. Thus \cmd
may have different definitions for each encoding.
\DeclareTextSymbol{\cmd}{code}{pos}
defines \cmd to print the character in the font position pos when encoding code
is active.
\DeclareTextAccent{\cmd}{code}{pos}
defines \cmd to be an accent command, using the character in font position pos
as the accent symbol, when encoding code is active.
\DeclareTextComposite{\cmd}{code}{letter}{pos}
\DeclareTextCompositeCommand{\cmd}{code}{letter}{def }
define the action of command \cmd followed by the single letter either to print the
character in font position pos or to execute the definition def. These declarations
are most useful with the T1 encoding, where many accented letters are separate