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encguide.tex
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encguide.tex
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% \iffalse meta-comment
%
% Copyright (C) 1993-2021
% The LaTeX3 Project and any individual authors listed elsewhere
% in this file.
%
% This file is part of the LaTeX base system.
% -------------------------------------------
%
% It may be distributed and/or modified under the
% conditions of the LaTeX Project Public License, either version 1.3c
% of this license or (at your option) any later version.
% The latest version of this license is in
% http://www.latex-project.org/lppl.txt
% and version 1.3c or later is part of all distributions of LaTeX
% version 2008 or later.
%
% This file has the LPPL maintenance status "maintained".
%
% The list of all files belonging to the LaTeX base distribution is
% given in the file `manifest.txt'. See also `legal.txt' for additional
% information.
%
% The list of derived (unpacked) files belonging to the distribution
% and covered by LPPL is defined by the unpacking scripts (with
% extension .ins) which are part of the distribution.
%
% \fi
%
\NeedsTeXFormat{LaTeX2e}[1995/12/01]
\documentclass{ltxguide}[1994/11/20]
\usepackage[T1]{fontenc}
\IfFileExists{lmodern.sty}{\usepackage{lmodern}}{}
\usepackage{textcomp}
\usepackage{url}
\usepackage{mflogo}
\addtolength\textheight{6\baselineskip}
\addtolength\topmargin{-2\baselineskip}
\newcommand\ttverb[1]{\texttt{\string#1}}
% for encodings
\providecommand{\Enc}[1]{\texttt{#1}}
% for packages
\providecommand{\Pkg}[1]{%
\textsf{#1}}
% for files
\providecommand{\File}[1]{%
\texttt{#1}}
% let's have meta values too
\providecommand{\meta}[1]{%
\ensuremath{\langle}\emph{#1}\ensuremath{\rangle}}
\usepackage{tabularx}
% eine Umgebung zur Darstellung von Kodierungen
%
% Argumente:
% #1: Name in LaTeX (z.B. OT1)
% #2: Name der Kodierung (z.B. TeX text)
% #3: Name des Autors (z.B. Don Knuth)
% #4: Bereich der benützten Glyphindizes
% #5: variable Positionen
% #6: Beispielzeichensatz
% #7: Referenz
%
% XXX add code to handle more than a single font example (e.g., larm1000,
% lbrm1000, and lcrm1000).
%
\newenvironment{encodinginfo}[7]%
{\noindent
\begin{tabularx}{\linewidth}{@{}l>{\raggedright\let\\\tabularnewline}X}%
\LaTeX{} name: & \texttt{#1}\\%
Public name: & #2\\%
Author: & #3\\%
Glyph slots used: & #4\\%
Variable slots: & #5\\%
Font example: & \def\@tempa{#6}\ifx\@tempa\@empty---%
\else\texttt{#6}\referenceftable{#6}\fi\\%
Further reference: & #7%
\end{tabularx}%
\par\nobreak
\vspace*{3pt}%
\quote
}%
{\endquote
\vspace{6pt}}
\makeatletter
\def\referenceftable#1{
\@ifundefined{r@fonttable:#1}%
\relax
{;\space encoding table on page~\pageref{fonttable:#1}}%
}
% font table macros mainly lifted from manmac.tex
\def\oct#1{\hbox{\rm\'{}\kern-.2em\it#1\/\kern.05em}}
\def\hex#1{\hbox{\rm\H{}\tt#1}}
\def\oddline#1{\cr\noalign{\nointerlineskip}
\multispan{19}\hrulefill&
\setbox0=\hbox{\lower 2.3pt\hbox{\hex{#1x}}}\smash{\box0}\cr
\noalign{\nointerlineskip}}
\def\evenline{\cr\noalign{\hrule}}
\def\chartstrut{\lower4.5pt\vbox to14pt{}}
\def\beginchart#1#2{$$\global\count@=0 #1
\halign to\hsize\bgroup
\chartstrut##\tabskip0pt plus10pt&
&\hfil##\hfil&\vrule##\cr
\lower6.5pt\null
&&\oct0&&\oct1&&\oct2&&\oct3&&\oct4&&\oct5&&\oct6&&\oct7&\evenline}
\def\endchart{\raise11.5pt\null&&&\hex 8&&\hex 9&&\hex A&&\hex B&
&\hex C&&\hex D&&\hex E&&\hex F&\cr\egroup$$}
\def\:{\setbox0=\hbox{\noboundary\char\count@\noboundary}%
\ifdim\ht0>7.5pt\reposition
\else\ifdim\dp0>2.5pt\reposition\fi\fi
\box0\global\advance\count@ by1 }
\def\reposition{\setbox0=\hbox{$\vcenter{\kern2pt\box0\kern2pt}$}}
\def\normalchart{%
&\oct{00x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline0
&\oct{01x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
&\oct{02x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline1
&\oct{03x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
&\oct{04x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline2
&\oct{05x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
&\oct{06x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline3
&\oct{07x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
&\oct{10x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline4
&\oct{11x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
&\oct{12x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline5
&\oct{13x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
&\oct{14x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline6
&\oct{15x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
&\oct{16x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline7
&\oct{17x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
\top}
\def\notophalf{}
\def\tophalf{%
%\noalign{\vskip 5pt\hrule}
&\oct{20x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline8
&\oct{21x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
&\oct{22x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline9
&\oct{23x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
&\oct{24x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline A
&\oct{25x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
&\oct{26x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline B
&\oct{27x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
&\oct{30x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline C
&\oct{31x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
&\oct{32x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline D
&\oct{33x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
&\oct{34x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline E
&\oct{35x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline
&\oct{36x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\oddline F
&\oct{37x}&&\:&&\:&&\:&&\:&&\:&&\:&&\:&&\:&\evenline}
\def\ftable#1#2{%
\batchmode
\font\X=#1%
\errorstopmode
\ifx\X\nullfont
\@warning{Font #1 not found, table omitted}
\else
\count@="80
\setbox0=\hbox{\X
\loop\char\count@\advance\count@ by1 \ifnum\count@<"100
\repeat}%
\ifdim\wd0>0pt \let\top\tophalf\else\let\top\notophalf\fi
\beginchart\X{\hfill\llap{\textbf{#1, \large#2}\label{fonttable:#1}}}\normalchart
\endchart\par\vfill
\fi}
\makeatother
\setcounter{tocdepth}{3}
\title{\LaTeX{} font encodings}
\author{Frank Mittelbach \and Robin
Fairbairns \and Werner Lemberg \and \LaTeX3 Project Team.}
\date{\copyright~Copyright 1995--2016 \\[5pt] 18 February 2016}
\begin{document}
\maketitle
\tableofcontents
\section{Introduction}
This document explains the ideas that underpin \LaTeX{} font
encodings and the constraints that apply when defining a new encoding; it
also lists the encodings that have already been defined.
\subsection{Encodings in \TeX{}}
\TeX{} (the program) implicitly recognises three sorts of encoding,
and all are (in a sense) discussed in the \TeX{}book~\cite{A-W:DKn86}:
\begin{itemize}
\item[1.] The input encoding, which specifies the meanings of characters
in files presented to \TeX{} for processing. The \TeX{}book
suggests that `your version of \TeX{} will recognise the characters
you type on your keyboard' (\TeX{} the program has provision for
static translations of input characters).
\end{itemize}
Such direct use of \TeX{}'s facilities is not the way modern
\LaTeX{} (or indeed any other \TeX{} macro package) is likely to deal
with input encodings. This document does not address the topic of
input encodings; the interested reader should examine the \LaTeX{}
base package \Pkg{inputenc} \cite[sec.~7.5.2, p.~357]{A-W:MG2004}.
\begin{itemize}
\item[2.] The token stream that \TeX{} processes internally. This stream
of \TeX{}'s consciousness is discussed in great detail in the
\TeX{}book.
\end{itemize}
Again, this document does not address the topic. \LaTeX's internal
character representation (\textsc{licr}) is well discussed in
\cite[sec.~7.11.2, p.~442]{A-W:MG2004}.
\begin{itemize}
\item[3.] The font encoding---i.e., the mapping of character codes to
glyphs in the fonts that are used to typeset \TeX{}'s output.
Again, a set of font encodings is enumerated in the \TeX{}book, but
that set has proved inadequate to the needs of modern multilingual
use of \LaTeX.
\end{itemize}
This document explains \emph{why} Knuth's original set of encodings is
inadequate to modern conditions, and discusses the issues that
surround the design and definition of new font encodings.
Font encodings are important for more than their r\^{o}le in mapping the
glyphs of the fonts to be used for typesetting: their glyph tables are
also the context in which \TeX{}'s hyphenation algorithm operates.
There are constraints imposed by \TeX{} that affect the way in which
new font encodings, for use in a multi-lingual environment, may be
structured (see section~\ref{sec:restrictions} for details).
\subsection{The history of \TeX{} font encodings}
Little attention was paid to font encodings prior to the arrival of
\TeX{}\,3. Up to that time, one used Donald Knuth's fonts (the
Computer Modern family, using the encodings we now refer to as \Enc{OT1} and
the \Enc{OM} series), or one was on one's own.
The Computer Modern text encoding raises problems in unmodified
\TeX{}, because hyphenation cannot break words containing
\verb"\accent" commands. Even in those Western European languages for
which the \Enc{OT1} encoding has symbols for the necessary
\verb"\accent"-based diacritics, this shortcoming ruins typesetting of
running text.
With the advent of \TeX{}\,3, with its ability to switch between
hyphenation pattern sets, it was clear that the situation could not
continue. Thus a group at the TUG Annual General Meeting in Cork,
Ireland, specified a uniform encoding for 256-glyph fonts, that
contains accented letters and non-\textsc{ascii} letters necessary to
express most Western European languages (and some Eastern European ones)
without recourse to the \verb"\accent" command.
This ``Cork'' encoding has since been realised in a series of fonts
designed with Metafont, in at least one font series that is available
both in Adobe Type 1 format and in OpenType format, % viz., Latin Modern
and in a number of virtual-font mappings of other font series.
Since the time of the Cork meeting, much effort has been devoted to
the design of encodings for text fonts to use with \TeX{}, and the
Cork encoding influenced the design of many such encodings.
Encodings for mathematical fonts have, in contrast, changed little
since Knuth's contributions. A TUG Technical Working Group was
established at the Cork meeting, whose aim was to define a set of
256-glyph encodings to regularise and extend Knuth's originals, using
ideas from several other fonts that had appeared since, and from the
known needs of researchers in mathematics and the mathematical sciences.
Independently, a first proposal (the so-called \emph{Aston proposal}) was worked
out by Justin Ziegler together with Frank Mittelbach and other members of the
\LaTeX3 project team~\cite{ziegler}. A first implementation of
this propsal was realized by Matthias Clasen und Ulrik
Vieth~\cite{clasen,clasen-vieth}.
However, the slow progress of these Mathematical encodings has been
overtaken by the addition (in the last decade or so) of a large number
of mathematical symbols to Unicode~\cite{beeton}; one can expect
further changes so that new public mathematical font encodings will
most likely be delayed still further.
\subsection{Further information}
For a general introduction to \LaTeX, including the new features of
\LaTeXe, you should read \emph{\LaTeXbook},
Leslie Lamport, Addison Wesley, 2nd~ed, 1994.
A more detailed description of the new features of \LaTeX, including an
overview of more than 200 packages and nearly 1000 ready to run examples, is
to be found in \emph{\LaTeXcomp{} second edition} by Frank Mittelbach and
Michel Goossens~\cite{A-W:MG2004}.
The \LaTeX{} project sponsored a report on Mathematical % spelt out in full
font encodings, which
is worth reading for its insight into the problems of defining the way
in which math is used: see~\cite{ziegler,clasen,clasen-vieth}.
The \LaTeX{} font selection scheme is based on \TeX, which is described
by its developer in \emph{The \TeX book}, Donald E.~Knuth, Addison
Wesley, 1986, revised in 1991 to include the features of \TeX~3.
For more information about \TeX{} and \LaTeX, please contact your local
\TeX{} Users Group, or the international \TeX{} Users Group
(\url{http://www.tug.org}).
\section{Existing font encodings}
This section lists the encodings currently assigned; for each
encoding, we list the registered (\LaTeX{}) name, the assigned purpose
of the encoding, and the author. Further details may list the code
positions used in the encoding, the \emph{variable slots} (see below),
an example font (for which a listing will be provided later in the
document if the relevant fonts are present), and a source for further
reference.
While the characteristic feature of an encoding is that each font
encoded according to the encoding should have the same glyph set,
there are some encodings (notably \Enc{OT1} and its descendants) in
which a few glyph code slots differ in their contents in different
fonts.
\subsection{Naming conventions}
Names for encoding schemes are strings of up to three letters (all
upper case) plus digits.
The \LaTeX3 project reserves the use of encoding names starting with the
following letters: |T| (standard 256-long text encodings), |TS|
(symbols that are designed to extend a corresponding |T| encoding),
|X| (text encodings that do not conform to the strict requirements for
|T| encodings), |M| (standard 256-long mathematical encodings), |S| (other
symbol encodings), |A| (other special applications), |OT| (standard
128-long text encodings), and |OM| (standard 128-long mathematical encodings).
Please do not use the above starting letters for non-portable
encodings. If new standard encodings emerge then we shall add them in
a later release of \LaTeX.
Encoding schemes which are local to a site or a system should start
with |L|, experimental encodings intended for wide distribution will
start with |E|, whilst |U| is for Unknown or Unclassified encodings.
\begin{quote}
\itshape We recommend that new encoding names should not be
introduced unless careful consideration and discussion in the user
community has confirmed the need for the encoding. If encodings have to
change from font to font, a number of problems arise, so it is best to
develop encodings that can be used with a large number of fonts in parallel.
This allows documents to be typeset using different fonts without problems.
The \Enc{TS1} encoding is a good example of a \emph{bad} encoding (even
though it was developed with the best intentions) as a huge number of fonts
can only implement parts of it. Similarly, the fact that the few sets of
available mathematical fonts (beside Computer Modern Math) nearly
all implement slightly different encodings is a huge source of
problems. Don't add to this if possible!
\end{quote}
\subsection{128$^+$ glyph encodings (text)}
The `OT' series of font encodings start with Donald Knuth's original
text encoding, that used for the text fonts in the earliest releases
of \TeX{} itself. The `O' of the encoding designator may be taken as
signifying `original', or just `old'.
\begin{encodinginfo}{OT1}
{\TeX{} text}
{Donald Ervin Knuth}
{0x00--0x7F}
{0x0B--0x0F, 0x24, 0x3C, 0x3E, 0x5C, 0x7B--0x7D}
% {0X--'177}
% {'13--'17, '44, '74, '76, '134, '173--'175}
{cmr10}
{\cite[p.427]{A-W:DKn86}}
Donald Knuth designed his font encoding (and hence his fonts) in a
very different environment from that which now pervades the \TeX{}
world: his (mainframe) computer had very little memory, there was
little experience in (or demand for) for multilingual technical
typesetting, and as a result it was appropriate to sacrifice
uniformity for efficiency.
Thus Knuth's original fonts differ slightly in some encoded slots:
for example, the glyphs \texttt{\string<}, \texttt{\string>},
\verb=\=, \verb={=, and \verb=}= are only available in the
typewriter fonts and the \textdollar{} and \textsterling{} signs
share the same position (in different font shapes).
This means that direct selection of these slots can produce
unpredictable results, e.g., typing \texttt{\string<} or
\verb=\symbol{'74}= in a document can yield `\textquestiondown'.
\end{encodinginfo}
\begin{encodinginfo}{OT2}
{UW cyrillic encoding}
{University of Washington}
{0x00--0x7F}
{---}
{wnr10}
{\cite{Beeton:TB6-3-124}}
Support for this encoding is available in the Cyrillic bundle although for
all practical purposes it is better to use one of the \Enc{T2} encodings.
\end{encodinginfo}
\begin{encodinginfo}{OT3}
{UW IPA encoding}
{University of Washington}
{0x00--0x7f}
{---}
{wsuipa10}
{\cite[p.149]{CorkGW:91}}
The \Enc{OT3} encoding was never really used with \LaTeXe{}
following the introduction of the TIPA system which offers much
better support for IPA. In particular, no \File{ot3enc.def}
file was ever produced.
\end{encodinginfo}
\begin{encodinginfo}{OT4}
{Polish text encoding}
{B.~Jackowski and M.~Ry\'cko} %% ? Marcin Woli\'nski
{0x00--0x7F, 0x81, 0x82, 0x86, 0x8A, 0x8B, 0x91, 0x99, 0x9B, 0xA1,
0xA2, 0xA6, 0xAA, 0xAB, 0xAE, 0xAF, 0xB1, 0xB9, 0xBB, 0xD3, 0xF3,
0xFF}
{0x0B--0x0F, 0x24, 0x3C, 0x3E, 0x5C, 0x7B--0x7D}
{plr10}
{---}
While Knuth included the means of typesetting the `lost L' (\L) in
his \Enc{OT1} encoding, he omitted the ogonek (\,\,\k{}), a diacritic
mark that is also needed in Polish text; hence the appearance, well
before the \Enc{T1} encoding, of fonts using this encoding.
\end{encodinginfo}
\begin{encodinginfo}{OT5}
{Not currently allocated}
{---}
{---}
{---}
{}
{---}
\end{encodinginfo}
\begin{encodinginfo}{OT6}
{Armenian text encoding}
{Serguei Dachian}
{0x03--0x0F, 0x13--0x7F}
{---}
{artmr10}
{---}
This encoding was allocated to permit use of Dachian's
Armenian fonts in a standard \LaTeX{} environment.
Because of license issues the \texttt{artmr} fonts are not necessarily
included in distributed \TeX{} installations (and for this reason the
corresponding encoding table is not shown below). However, the fonts
and the support macros can be found on the CTAN archives (look for
\texttt{armtex}).
\end{encodinginfo}
\subsection{256 glyph encodings (text)}
\begin{encodinginfo}{T1}
{Cork encoding}
{Euro \TeX{} conference at Cork}
{0x00--0xFF}
{---}
{ecrm1000}
{\cite[p.514]{tub:MFe90}, \cite[p.99]{Knappen:TB17-2-96}}
The Cork encoding was developed so that advantage could be taken of
the (then) new facilities of \TeX{}\,3, allowing hyphenation of
most Western European (and some Eastern European) languages in an
unmodified version of \TeX{}.
The encoding was developed in the absence of any extant effort at
font design, but instances written in Metafont (the `EC' fonts), and
more recently Adobe Type 1 instances of the same fonts have become
available.
Substantial (but incomplete) instances have also been developed,
which use virtual fonts. These latter instances map either Knuth's
original (OT1-encoded) fonts, or commercial fonts that contain the
Adobe `standard' set of 224 glyphs.
\end{encodinginfo}
\begin{encodinginfo}
{T2A, T2B, T2C}
{Cyrillic encodings}
{The CyrTUG font team}
{0x00--0xFF}
{--- (within each encoding)}
{larm1000}
{\cite{Berdnikov:eurotex-98}}
There are too many glyphs in the full Cyrillic complement of
languages for all of them to be covered by a single
\LaTeX{}-compliant encoding (the lower half of each
\Enc{T2}~encoding is identical to that of \Enc{T1}, in order that
each should be a conforming \LaTeX{} encoding~--- see
section~\ref{sec:restrictions}). The approach taken is
therefore to develop a single encoding, \Enc{X2} (see \ref{sec:extendedenc})
which contains all the glyphs needed for the full set of
languages, and then to derive the three \LaTeX{}-complaint
\Enc{T2}-family encodings using the \Enc{X2} set together with that of
\Enc{T1}.
\end{encodinginfo}
\begin{encodinginfo}{T3}
{IPA encoding}
{FUKUI Rei, University of Tokyo}
{0x00--0xFF}
{---}
{tipa10}
{\cite[p.102]{Rei:TB17-2-102}}
The \Enc{T3} encoding (and associated macros) provides the glyphs required
in phonetic description according to current International Phonetic
Association recommendations \cite{ipa}.
The \Enc{T3} encoding does \emph{not fulfil} the requirements for \Enc{T}
encodings---the name is a historical accident. The correct name would be
\Enc{X3}, but due to the fact that this font family has been used under its
current encoding name for a long time, the name will not change for
compatibility reasons.
\end{encodinginfo}
\begin{encodinginfo}{T4}
{African Latin (fc)} % public name
{J\"org Knappen} % author name
{0x00--0xFF} % range(s) of slots used for glyphs
{0x24} % range(s) of slots with variable glyphs if any
{fcr10} % name of an example font
{\cite{tub:JKn93}}
The African Latin fonts contain in their lower half (0--127) the same
characters as the European Latin (T1-encoded) Fonts, while in their
upper half (128--255) they
contain letters and symbols for African languages that use extended
Latin alphabets.
Due to lack of space, J\"org had to play the unfortunate trick of
assigning \verb=\textdollar= and \verb=\textsterling=
the same position; users should take these characters
from the text companion font, if they are needed. Instead of defining
a lot of new control sequences for the single letters, there are three
accent-like control sequences with general purpose:
\verb=\m= (Modified-1),
\verb=\M= (Modified-2) and
\verb=\B= (Barred).
Most standard \LaTeX{} encoding-dependent commands
work. However, the Icelandic special letters are not available and `best
replacements' for \verb=\Th=, \verb=\th=, and \verb=\dh=
are used (barred T and d resp.).
\end{encodinginfo}
\begin{encodinginfo}{T5}
{Vietnamese encoding}
{Werner Lemberg and
Vladimir Volovich}
{0x00--0xFF}
{---}
{vnr10}
{\cite{vnr}}
The \Enc{T5} encoding was developed for Vietnamese. Again, this encoding
\emph{does not} conform to the requirements for a \Enc{T}-encoding
because its large number of accented letters prevent the \verb=\lccode= and
\verb=\uccode= mapping requirements for \Enc{T} encodings from being
fulfilled. However, since the Vietnamese language does not
use word division in typesetting so that this requirement is
actually not important for this particular language.
Since every glyph used in Vietnamese text is internally
represented as \textsc{licr} macros, the commands \verb=\MakeUppercase= and
\verb=\MakeLowercase= still work as expected (as they change the case of the
\textsc{ascii} characters in \textsc{licr} definitions).
\end{encodinginfo}
\begin{encodinginfo}
{T6}
{Armenian}
{---}
{---}
{---}
{}
{---}
This encoding is reserved to permit future expansion of Armenian
\TeX{} to use 256-character (hyphenatable) fonts.
\end{encodinginfo}
\begin{encodinginfo}{T7}
{Greek encoding}
{---}
{---}
{---}
{}
{---}
The name is already reserved for a 256 glyph greek encoding. The encoding
itself hasn't been defined so far.
\end{encodinginfo}
\subsection{256$^-$ glyph encodings (text symbols)}
\begin{encodinginfo}{TS1}
{Text Companion encoding (Cork)}
{J\"org Knappen}
{0x00--0x0D, 0x12, 0x15, 0x16, 0x18--0x1D, 0x20, 0x24, 0x27, 0x2A,
0x2C--0x3A, 0x3C--0x3E, 0x4D, 0x4F, 0x57, 0x5B, 0x5D--0x60,
0x62--0x64, 0x6C--0x6E, 0x7E--0xBF, 0xD6, 0xF6}
{---}
{tcrm1000}
{\cite{Knappen:TB17-2-96}}
The text symbol encoding offers access to symbolic glyphs that are
commonly used in text (for a variety of reasons), and whose style
should vary with the text that surrounds them.
Unfortunately, the \Enc{TS1} encoding was developed without
reference to the glyphs available in existing commercial fonts.
As a result, only font families
explicitly developed for \TeX{} (i.e., typically originating with
\MF{}) actually contain all glyphs required by the \Enc{TS1}
encoding. Most other font families (whether free or commercial)
often only provide half of the set%
%%
%% don't show the comment if the tables are not generated
%%
\expandafter\ifx\csname r@fonttable:tcrm1000\endcsname\relax
\else
\expandafter\ifx\csname r@fonttable:ptmr8c\endcsname\relax
\else
\space (compare the two tables for \Enc{TS1} on
pages~\pageref{fonttable:tcrm1000}
and~\pageref{fonttable:ptmr8c})%
\fi
\fi.
To improve this situation somewhat, NFSS provides a way to define encoding
subsets on a per family basis in the \Pkg{textcomp} package (which
package offers support for the \Enc{TS1} encoding).
\end{encodinginfo}
\begin{encodinginfo}{TS3}
{IPA symbol encoding}
{FUKUI Rei, University of Tokyo}
{0x00--0x0A, 0x20--0x49, 0x50--0x56, 0x70--0x7B}
{---}
{tipx10}
{\cite{Rei:TB17-2-102}}
The \Enc{TS3} encoding (together with the \Enc{T3} encoding) provides the
glyphs for typesetting phonetic transcriptions following the
guidelines of the International Phonetic Association \cite{ipa}. Support
is offered through the \Pkg{tipa} package.
\end{encodinginfo}
\subsection{256 glyph encodings (text extended)}
\label{sec:extendedenc}
\begin{encodinginfo}
{X2}
{Cyrillic glyph container}
{The CyrTUG font team}
{0x00--0xFF}
{---}
{rxrm1000}
{\cite{Berdnikov:eurotex-98}}
This encoding specifies the glyph container for Cyrillic characters,
which is used in specifying the \Enc{T2A}, \Enc{T2B} and \Enc{T2C} encodings.
\end{encodinginfo}
\subsection{128$^+$ glyph encodings (mathematics)}
\begin{encodinginfo}{OML}
{\TeX{} math italic}
{Donald Ervin Knuth}
{0x00--0x7F}
{---}
{cmmi10}
{\cite[p.430]{A-W:DKn86}}
The \Enc{OML} encoding contains italic Latin and Greek letters for
use in mathematical formulas (typically used for variables) together
with some symbols.
\end{encodinginfo}
\begin{encodinginfo}{OMS}
{\TeX{} math symbol}
{Donald Ervin Knuth}
{0x00--0x7F}
{---}
{cmsy10}
{\cite[p.431]{A-W:DKn86}}
The \Enc{OMS} encoding contains basic mathematical symbols,
together with an uppercase ``calligraphic'' Latin alphabet.
\end{encodinginfo}
\begin{encodinginfo}{OMX}
{\TeX{} math extension}
{Donald Ervin Knuth}
{0x00--0x7F}
{---}
{cmex10}
{\cite[p.432]{A-W:DKn86}}
\Enc{OMS} encodes mathematical symbols with variable sizes, such as
the $\sum$ sign, which changes its size if used in displayed
formulas, and the construction parts for
brackets, braces and radicals, etc., which can stretch to accommodate
the thing they're enclosing.
\end{encodinginfo}
\subsection{256 glyph encodings (mathematics)}
So far there are no 256 glyph mathematical encodings. A proposal is
given in \cite{ziegler}.
\subsection{Other encodings}
\begin{encodinginfo}
{C..}
{CJK encodings}
{Werner Lemberg}
{0x00--0xFF}
{---}
{} % no font, of course
{\cite{CJK}}
The \Pkg{CJK} package defines a number of encodings which access Chinese,
Japanese and Korean fonts.
\end{encodinginfo}
\begin{encodinginfo}
{E..}
{Experimental encodings}
{---}
{0x00--0xFF}
{all}
{}
{\cite[p.416]{A-W:MG2004}}
As the name indicates, encodings starting with the letter \Enc{E} are
intended for experimental encodings, that are still likely to change.
\end{encodinginfo}
\begin{encodinginfo}{L..}
{Local encoding (site dependent)}
{---}
{0x00--0xFF}
{all}
{}
{\cite[p.416]{A-W:MG2004}}
`Local' encodings provide the means to develop representation
techniques that are suited to a particular \TeX{} environment. While
the developer has freedom to specify their encoding as he or she
pleases, there is a strong incentive to obey the \LaTeX{} rules for
encodings, since it will otherwise be difficult to compose text using
the encoding.
At least it was the intention that \Enc{L..} encodings are local and
site dependent. However, a number of such encodings became generally
used without ever getting a different name allocated.
\end{encodinginfo}
\begin{encodinginfo}{LY1}
{Y\&Y 256 glyph encoding}
{Berthold Horn}
{0x00--0x08, 0x0C, 0x10, 0x12--0xFF}
{\emph{believed none}}
{ptmr8y}
{\cite[p.416]{A-W:MG2004}}
This is an alternative to the \Enc{T1} encoding developed by Y\&Y and
used in their commercial \TeX{} implementation.
\end{encodinginfo}
\begin{encodinginfo}{LV1}
{MicroPress encoding}
{Michael Vulis}
{\emph{unknown}}
{\emph{unknown}}
{}
{\cite[p.416]{A-W:MG2004}}
This is an encoding developed by MicroPress and used for some of their
fonts.
\end{encodinginfo}
\begin{encodinginfo}{LGR}
{Greek 256 glyph encoding}
{\emph{unknown}}
{0x00--0xFF}
{\emph{believed none}}
{grmn1000}
{\cite[p.575]{A-W:MG2004}}
Currently the main encoding in use for the Greek language.
This encoding doesn't conform to the restrictions for
\Enc{T}-encodings described in section~\ref{sec:restrictions} on
page~\pageref{sec:restrictions} as it doesn't have \textsc{ascii}
glyphs at all.
\end{encodinginfo}
\begin{encodinginfo}
{PD1}
{PDF DocEncoding}
{Adobe}
{0x08--0x0A, 0x0C, 0x0D, 0x18--0x7E, 0x80--0x9E, 0xA0--0xAE, 0xB0--0xFF}
{---}
{}
{\cite{Adobe:PDF-1.6}, \cite{hyperref}}
The \Enc{PD1} encoding is a virtual encoding with 256 glyphs needed to
produce bookmarks and similar text in PDF document generated with pdf\LaTeX.
The encoding is ``virtual'' because by design there are no \TeX{}
fonts that cover \Enc{PD1}. Details can be found in appendix D.1
of~\cite{Adobe:PDF-1.6}.
\end{encodinginfo}
\begin{encodinginfo}
{PU}
{PDF Unicode Encoding}
{Adobe}
{---}
{---}
{}
{\cite{Adobe:PDF-1.6}, \cite{hyperref}}
Another virtual encoding (with more than 600 characters) for
Unicode-encoded bookmarks in PDF documents.
\end{encodinginfo}
\begin{encodinginfo}{U}
{Unknown encoding}
{---}
{potentially 0x00-0xFF}
{all}
{wasy10}
{\cite[p.416]{A-W:MG2004}}
This encoding should be used for fonts that resist classification,
e.g., when it is clear that there will never be more than one font
using the same encoding.
\end{encodinginfo}
\section{Restrictions}
\label{sec:restrictions}
\subsection{Required glyphs for general text encodings}
Encodings that are supposed to be used with \LaTeX{} for `general
purpose text fonts' need to have certain fixed glyphs in certain
encoding slots. A `general purpose text font' is one intended for
arbitrary natural language text and not just within special
environments (such as the phonetic alphabet) or just for typesetting
individual symbols (e.g., the text companion font with encoding
\Enc{TS1}).
This is the case for the following glyphs that have to be in their
\textsc{ascii} positions for general purpose text encodings:
\begin{center}
\begin{tabular}[t]{cc}
Glyph & Position \\ \hline
! & \number`\! \\
' & \number`\' \\
( & \number`\( \\
) & \number`\) \\
\relax* & \number`\* \\
+ & \number`\+ \\
, & \number`\, \\
- & \number`\- \\
. & \number`\. \\
/ & \number`\/ \\
0 \ldots\ 9 & \number`\0\ to \number`\9 \\
\end{tabular}
\quad
\begin{tabular}[t]{cc}
Glyph & Position \\ \hline
: & \number`\: \\
; & \number`\; \\
= & \number`\= \\
? & \number`\? \\
@ & \number`\@ \\
A \ldots\ Z & \number`\A\ to \number`\Z \\
\relax[ & \number`\[ \\
] & \number`\] \\
` & \number`\` \\
a \ldots\ z & \number`\a\ to \number`\z \\
\end{tabular}
\quad
\begin{tabular}[t]{cc}
Glyph\footnotemark & Position \\ \hline
< & \number`\< \\
> & \number`\> \\
\string| & \number`\| \\
\end{tabular}\footnotetext{The requirement for these three glyphs is
violated in the Latin alphabet \Enc{OT} encodings.}
\end{center}
In addition the following glyphs have to be present
somewhere\footnote{The position in this case is not important as they
are generated from ligature programs.} in the encoding together with
corresponding ligature programs to generate them:
\begin{center}
\begin{tabular}[t]{cc}
Glyph & Ligature program \\ \hline
`` & \texttt{`\/`} \\
'' & \texttt{'\/'} \\
-- & \texttt{-\/-} \\
--- & \texttt{-\/-\/-} \\
\end{tabular}
\end{center}
This is $33 + 2 * 26 = 85$ positions ``required'', which leaves 171
positions free.
If there are free slots available then adding all or some of the
diacritics would be the best way to fill them.
If there are insufficient slots for the characters needed, a possible
technique is to create a subsidiary encoding, and to move non-letter
characters to it. Since only ``letters'' take part in the hyphenation
algorithm, this technique doesn't affect the appearance of the typeset
result.