\relax
\documentclass[twocolumn]{article}
\usepackage[specification]{fontdoc}[2001/06/01]

\DeclareRobustCommand\cs[1]{\texttt{\char`\\#1}}

\showbranches

\begin{document}

\title{\texttt{OT1} encoding draft specification}
\author{Lars Hellstr\"om}
\date{2001/09/09}
\maketitle

\begin{abstract}
  The \texttt{OT1} encoding is an attempt to describe the encoding of 
  the text fonts in Donald~E.~Knuth's \emph{Computer Modern} family 
  of fonts~\cite{ComputerModern}. This is an impossibile goal, since 
  these fonts present no less than five different encodings, but they 
  are nontheless largely treated by \LaTeX\ as having identical 
  encodings. Due to the ambiguities this creates, and in view of that 
  the \texttt{T1} encoding supersedes \texttt{OT1} as text font 
  encoding, there is little point in using the text commands for 
  distiguishing mandatory features of \texttt{OT1} from the ordinary.
  
  \texttt{OT1} is however also used as a math font encoding (to go 
  with \texttt{OML}, \texttt{OMS}, and \texttt{OMX}), and that use is 
  today the by far most important since there is no obvious alternative 
  to the standard math font set-up. Therefore this specification 
  considers a feature of the encoding to be mandatory if it is 
  (i)~necessary for the standard math set-up or (ii)~is a text feature 
  which works for all encoding variants.
\end{abstract}

\encoding
\needsfontinstversion{1.918}



\begincomment
\section{Encoding variants}

This document aims to record all the encoding variations that are 
present within the set of fonts classified by \LaTeX\ as having the 
\texttt{OT1} encoding. It turns out that they can all be described 
using only two parameters. One of these might be called 
`\textit{ligaturing}' as one factor it affects is how many ligatures 
there will be in the font. The other parameter is best called 
`\textit{italicizing}' as it is different between italic and 
non-italic fonts. Most of the Computer Modern fonts have 
\(\mathit{ligaturing} = 2\) and \(\mathit{italicizing} = 0\).

\endcomment
\setint{ligaturing}{2}
\setint{italicizing}{0}


\begincomment


\section{Mandatory characters}

\subsection{Latin letters}
\endcomment

\nextslot{16}
\setslot{dotlessi}
  \Unicode{0131}{LATIN SMALL LETTER DOTLESS I}
  \comment{A dotless i `\i', used to produce accented letters such as
     `\=\i'. It is not used for math.}
\endsetslot

\setslot{dotlessj}
  \Unicode{F6BE}{LATIN SMALL LETTER DOTLESS J}
  \comment{A dotless j `\j', used to produce accented letters such as
     `\=\j'. It is not used for math. The Unicode standard does not 
     define this character, but Adobe has assigned code point 
     \texttt{U+F6BE} (which is in the private use subarea assigned by 
     Adobe) to it.}
\endsetslot

\nextslot{25}
\setslot{germandbls}
  \Unicode{00DF}{LATIN SMALL LETTER SHARP S}
  \comment{This slot is not used in math.}
\endsetslot

\setslot{ae}
  \Unicode{00E6}{LATIN SMALL LETTER AE}
  \comment{This slot is not used in math.}
\endsetslot

\setslot{oe}
  \Unicode{0153}{LATIN SMALL LIGATURE OE}
  \comment{This is a single letter, and should not be faked with `oe'. 
     It is not used in math.}
\endsetslot

\setslot{oslash}
  \Unicode{00F8}{LATIN SMALL LETTER O WITH STROKE}
  \comment{This slot is not used in math.}
\endsetslot

\setslot{AE}
  \Unicode{00C6}{LATIN CAPITAL LETTER AE}
  \comment{This slot is not used in math.}
\endsetslot

\setslot{OE}
  \Unicode{0152}{LATIN CAPITAL LIGATURE OE}
  \comment{This is a single letter, and should not be faked with 
     `OE'. It is not used in math.}
\endsetslot

\setslot{Oslash}
  \Unicode{00D8}{LATIN CAPITAL LETTER O WITH STROKE}
  \comment{This slot is not used in math.}
\endsetslot


\nextslot{65}
\setslot{A}
  \Unicode{0041}{LATIN CAPITAL LETTER A}
  \label{A}
\endsetslot

\setslot{B}
  \Unicode{0042}{LATIN CAPITAL LETTER B}
\endsetslot

\setslot{C}
  \Unicode{0043}{LATIN CAPITAL LETTER C}
\endsetslot

\setslot{D}
  \Unicode{0044}{LATIN CAPITAL LETTER D}
\endsetslot

\setslot{E}
  \Unicode{0045}{LATIN CAPITAL LETTER E}
\endsetslot

\setslot{F}
  \Unicode{0046}{LATIN CAPITAL LETTER F}
\endsetslot

\setslot{G}
  \Unicode{0047}{LATIN CAPITAL LETTER G}
\endsetslot

\setslot{H}
  \Unicode{0048}{LATIN CAPITAL LETTER H}
\endsetslot

\setslot{I}
  \Unicode{0049}{LATIN CAPITAL LETTER I}
\endsetslot

\setslot{J}
  \Unicode{004A}{LATIN CAPITAL LETTER J}
\endsetslot

\setslot{K}
  \Unicode{004B}{LATIN CAPITAL LETTER K}
\endsetslot

\setslot{L}
  \Unicode{004C}{LATIN CAPITAL LETTER L}
\endsetslot

\setslot{M}
  \Unicode{004D}{LATIN CAPITAL LETTER M}
\endsetslot

\setslot{N}
  \Unicode{004E}{LATIN CAPITAL LETTER N}
\endsetslot

\setslot{O}
  \Unicode{004F}{LATIN CAPITAL LETTER O}
\endsetslot

\setslot{P}
  \Unicode{0050}{LATIN CAPITAL LETTER P}
\endsetslot

\setslot{Q}
  \Unicode{0051}{LATIN CAPITAL LETTER Q}
\endsetslot

\setslot{R}
  \Unicode{0052}{LATIN CAPITAL LETTER R}
\endsetslot

\setslot{S}
  \Unicode{0053}{LATIN CAPITAL LETTER S}
\endsetslot

\setslot{T}
  \Unicode{0054}{LATIN CAPITAL LETTER T}
\endsetslot

\setslot{U}
  \Unicode{0055}{LATIN CAPITAL LETTER U}
\endsetslot

\setslot{V}
  \Unicode{0056}{LATIN CAPITAL LETTER V}
\endsetslot

\setslot{W}
  \Unicode{0057}{LATIN CAPITAL LETTER W}
\endsetslot

\setslot{X}
  \Unicode{0058}{LATIN CAPITAL LETTER X}
\endsetslot

\setslot{Y}
  \Unicode{0059}{LATIN CAPITAL LETTER Y}
  \label{Y}
\endsetslot

\setslot{Z}
  \Unicode{005A}{LATIN CAPITAL LETTER Z}
\endsetslot


\nextslot{97}
\setslot{a}
  \Unicode{0061}{LATIN SMALL LETTER A}
\endsetslot

\setslot{b}
  \Unicode{0062}{LATIN SMALL LETTER B}
\endsetslot

\setslot{c}
  \Unicode{0063}{LATIN SMALL LETTER C}
\endsetslot

\setslot{d}
  \Unicode{0064}{LATIN SMALL LETTER D}
\endsetslot

\setslot{e}
  \Unicode{0065}{LATIN SMALL LETTER E}
\endsetslot

\setslot{f}
  \Unicode{0066}{LATIN SMALL LETTER F}
  \ifnumber{\int{ligaturing}}={2}\then
    \ligature{LIG}{f}{ff}
    \ligature{LIG}{i}{fi}
    \ligature{LIG}{l}{fl}
  \Fi
\endsetslot

\setslot{g}
  \Unicode{0067}{LATIN SMALL LETTER G}
\endsetslot

\setslot{h}
  \Unicode{0068}{LATIN SMALL LETTER H}
\endsetslot

\setslot{i}
  \Unicode{0069}{LATIN SMALL LETTER I}
\endsetslot

\setslot{j}
  \Unicode{006A}{LATIN SMALL LETTER J}
\endsetslot

\setslot{k}
  \Unicode{006B}{LATIN SMALL LETTER K}
\endsetslot

\setslot{l}
  \Unicode{006C}{LATIN SMALL LETTER L}
\endsetslot

\setslot{m}
  \Unicode{006D}{LATIN SMALL LETTER M}
\endsetslot

\setslot{n}
  \Unicode{006E}{LATIN SMALL LETTER N}
\endsetslot

\setslot{o}
  \Unicode{006F}{LATIN SMALL LETTER O}
\endsetslot

\setslot{p}
  \Unicode{0070}{LATIN SMALL LETTER P}
\endsetslot

\setslot{q}
  \Unicode{0071}{LATIN SMALL LETTER Q}
\endsetslot

\setslot{r}
  \Unicode{0072}{LATIN SMALL LETTER R}
\endsetslot

\setslot{s}
  \Unicode{0073}{LATIN SMALL LETTER S}
\endsetslot

\setslot{t}
  \Unicode{0074}{LATIN SMALL LETTER T}
\endsetslot

\setslot{u}
  \Unicode{0075}{LATIN SMALL LETTER U}
\endsetslot

\setslot{v}
  \Unicode{0076}{LATIN SMALL LETTER V}
\endsetslot

\setslot{w}
  \Unicode{0077}{LATIN SMALL LETTER W}
\endsetslot

\setslot{x}
  \Unicode{0078}{LATIN SMALL LETTER X}
\endsetslot

\setslot{y}
  \Unicode{0079}{LATIN SMALL LETTER Y}
\endsetslot

\setslot{z}
  \Unicode{007A}{LATIN SMALL LETTER Z}
\endsetslot


\begincomment
\subsection{Greek letters}
\endcomment

\nextslot{0}
\setslot{Gamma}
  \Unicode{0393}{GREEK CAPITAL LETTER GAMMA}
\endsetslot

\setslot{Delta}
  \Unicode{0394}{GREEK CAPITAL LETTER DELTA}
\endsetslot

\setslot{Theta}
  \Unicode{0398}{GREEK CAPITAL LETTER THETA}
\endsetslot

\setslot{Lambda}
  \Unicode{039B}{GREEK CAPITAL LETTER LAMBDA}
  % Unicode's preferred name for this character seems to be
  % GREEK CAPITAL LETTER LAMDA, i.e., without the `B'. Why?
  % GREEK CAPITAL LETTER LAMBDA is listed as an alternative name.
\endsetslot

\setslot{Xi}
  \Unicode{039E}{GREEK CAPITAL LETTER XI}
\endsetslot

\setslot{Pi}
  \Unicode{03A0}{GREEK CAPITAL LETTER PI}
\endsetslot

\setslot{Sigma}
  \Unicode{03A3}{GREEK CAPITAL LETTER SIGMA}
\endsetslot

\setslot{Upsilon1}
  \Unicode{03D2}{GREEK UPSILON WITH HOOK SYMBOL}
  \comment{This is primarily a math character and it is should 
    be visually distinct from the character in slot~\ref{Y}. This is 
    not generally the case for the normal Upsilon 
    \textunicode{03A5}{GREEK CAPITAL LETTER UPSILON}, which is by 
    the way what usually has the glyph name \texttt{Upsilon}. 
    An argument for the latter is however that all the purely 
    mathematical Upsilons that exist in the Unicode standard are 
    described as variants of the non-hook character.}
\endsetslot

\setslot{Phi}
  \Unicode{03A6}{GREEK CAPITAL LETTER PHI}
\endsetslot

\setslot{Psi}
  \Unicode{03A8}{GREEK CAPITAL LETTER PSI}
\endsetslot

\setslot{Omega}
  \Unicode{03A9}{GREEK CAPITAL LETTER OMEGA}
\endsetslot


\begincomment
\subsection{Digits}
\endcomment

\nextslot{48}
\setslot{zero}
  \Unicode{0030}{DIGIT ZERO}
\endsetslot

\setslot{one}
  \Unicode{0031}{DIGIT ONE}
\endsetslot

\setslot{two}
  \Unicode{0032}{DIGIT TWO}
\endsetslot

\setslot{three}
  \Unicode{0033}{DIGIT THREE}
\endsetslot

\setslot{four}
  \Unicode{0034}{DIGIT FOUR}
\endsetslot

\setslot{five}
  \Unicode{0035}{DIGIT FIVE}
\endsetslot

\setslot{six}
  \Unicode{0036}{DIGIT SIX}
\endsetslot

\setslot{seven}
  \Unicode{0037}{DIGIT SEVEN}
\endsetslot

\setslot{eight}
  \Unicode{0038}{DIGIT EIGHT}
\endsetslot

\setslot{nine}
  \Unicode{0039}{DIGIT NINE}
\endsetslot


\begincomment
\subsection{Accents}
\endcomment

\nextslot{18}
\setslot{grave}
   \Unicode{0300}{COMBINING GRAVE ACCENT}
\endsetslot

\setslot{acute}
  \Unicode{0301}{COMBINING ACUTE ACCENT}
\endsetslot

\setslot{caron}
  \Unicode{030C}{COMBINING CARON}
  \comment{The caron or h\'a\v cek accent `\v{}'.}
\endsetslot

\setslot{breve}
  \Unicode{0306}{COMBINING BREVE}
\endsetslot

\setslot{macron}
  \Unicode{0304}{COMBINING MACRON}
\endsetslot

\setslot{ring}
  \Unicode{030A}{COMBINING RING ABOVE}
  \comment{The text definition of `\verb|\r{A}|' assumes that this 
    glyph has the same width as that in slot~\ref{A}.}
\endsetslot

\setslot{cedilla}
  \Unicode{0327}{COMBINING CEDILLA}
  \comment{This slot is not required for math, but is used by 
    the \cs{c} \LaTeX\ command.}
\endsetslot


\nextslot{94}
\setslot{circumflex}
  \Unicode{0302}{COMBINING CIRCUMFLEX ACCENT}
  \Unicode{005E}{CIRCUMFLEX ACCENT}
\endsetslot

\ifnumber{\int{ligaturing}}>{0}\then

\setslot{dotaccent}
  \Unicode{0307}{COMBINING DOT ABOVE}
  \label{dotaccent}
\endsetslot

\begincomment
\par\medskip
Note that the \(\mathit{ligaturing} = 0\) assignment to 
slot~\ref{underscore} is ordinary, not mandatory.
\endcomment

\Fi


\nextslot{126}
\setslot{tilde}
  \Unicode{0303}{COMBINING TILDE}
  \Unicode{007E}{TILDE}
\endsetslot

\setslot{dieresis}
  \Unicode{0308}{COMBINING DIAERESIS}
\endsetslot


\begincomment
\subsection{Symbols}
\endcomment

\nextslot{33}
\setslot{exclam}
  \Unicode{0021}{EXCLAMATION MARK}
  \Ligature{LIG}{quoteleft}{exclamdown}
\endsetslot

\skipslots{1}

\setslot{numbersign}
  \Unicode{0023}{NUMBER SIGN}
  \comment{This slot is not used for math.}
\endsetslot

\ifnumber{\int{italicizing}}={0}\then

\setslot{dollar}
  \Unicode{0024}{DOLLAR SIGN}
\endsetslot

\Else

\setslot{sterling}
  \Unicode{00A3}{POUND SIGN}
\endsetslot

\Fi

\setslot{percent}
  \Unicode{0025}{PERCENT SIGN}
  \comment{This slot is not used for math.}
\endsetslot

\setslot{ampersand}
  \Unicode{0026}{AMPERSAND}
  \comment{This slot is not used for math.}
\endsetslot

\setslot{quoteright}
  \Unicode{2019}{RIGHT SINGLE QUOTATION MARK}
  \comment{This slot is not used for math.}
  \ifnumber{\int{ligaturing}}>{0}\then
    \Ligature{LIG}{quoteright}{quotedblright}
  \Fi
\endsetslot

\setslot{parenleft}
  \Unicode{0028}{LEFT PARENTHESIS}
\endsetslot

\setslot{parenright}
  \Unicode{0029}{RIGHT PARENTHESIS}
\endsetslot

\setslot{asterisk}
  \Unicode{002A}{ASTERISK}
  \comment{This slot is not used for math.}
\endsetslot

\setslot{plus}
  \Unicode{002B}{PLUS SIGN}
\endsetslot

\setslot{comma}
  \Unicode{002C}{COMMA}
  \comment{This slot is not used for math.}
\endsetslot

\setslot{hyphen}
  \Unicode{002D}{HYPHEN-MINUS}
  \comment{This slot is not used for math.}
  \ifnumber{\int{ligaturing}}>{0}\then
    \Ligature{LIG}{hyphen}{endash}
  \Fi
\endsetslot

\setslot{period}
  \Unicode{002E}{FULL STOP}
  \comment{This slot is not used for math.}
\endsetslot

\setslot{slash}
  \Unicode{002F}{SOLIDUS}
\endsetslot

\nextslot{58}
\setslot{colon}
  \Unicode{003A}{COLON}
\endsetslot

\setslot{semicolon}
  \Unicode{003B}{SEMICOLON}
\endsetslot

\skipslots{1}

\setslot{equal}
  \Unicode{003D}{EQUALS SIGN}
\endsetslot

\skipslots{1}

\setslot{question}
  \Unicode{003F}{QUESTION MARK}
  \Ligature{LIG}{quoteleft}{questiondown}
\endsetslot

\setslot{at}
  \Unicode{0040}{COMMERCIAL AT}
  \comment{This slot is not used for math.}
\endsetslot

\nextslot{91}
\setslot{bracketleft}
  \Unicode{005B}{LEFT SQUARE BRACKET}
\endsetslot

\skipslots{1}

\setslot{bracketright}
  \Unicode{005D}{RIGHT SQUARE BRACKET}
\endsetslot

\nextslot{96}
\setslot{quoteleft}
  \Unicode{2018}{LEFT SINGLE QUOTATION MARK}
  \comment{This slot is not used for math.}
  \ifnumber{\int{ligaturing}}>{0}\then
    \Ligature{LIG}{quoteleft}{quotedblleft}
  \Fi
\endsetslot



\begincomment
\section{Ordinary characters}

\subsection{Letters}
\endcomment

\ifnumber{\int{ligaturing}}={2}\then

\nextslot{11}
\setslot{ff}
  \Unicode{FB00}{LATIN SMALL LIGATURE FF}
  \comment{This glyph should be two characters wide in a monowidth 
    font.}
  \ligature{LIG}{i}{ffi}
  \ligature{LIG}{l}{ffl}
\endsetslot

\setslot{fi}
  \Unicode{FB01}{LATIN SMALL LIGATURE FI}
  \comment{This glyph should be two characters wide in a monowidth 
    font.}
\endsetslot

\setslot{fl}
  \Unicode{FB02}{LATIN SMALL LIGATURE FL}
  \comment{This glyph should be two characters wide in a monowidth 
    font.}
\endsetslot

\setslot{ffi}
  \Unicode{FB03}{LATIN SMALL LIGATURE FFI}
  \comment{This glyph should be three characters wide in a monowidth 
    font.}
\endsetslot

\setslot{ffl}
  \Unicode{FB04}{LATIN SMALL LIGATURE FFL}
  \comment{This glyph should be three characters wide in a monowidth 
    font.}
\endsetslot

\Fi

\nextslot{"8A}
\setslot{Lslash}
  \Unicode{0141}{LATIN CAPITAL LETTER L WITH STROKE}
  \comment{The letter `\L'.}
\endsetslot

\nextslot{"AA}
\setslot{lslash}
  \Unicode{0142}{LATIN SMALL LETTER L WITH STROKE}
  \comment{The letter `\l'.}
\endsetslot


\begincomment
\subsection{Accents}
\endcomment

\ifnumber{\int{ligaturing}}>{0}\then

\nextslot{125}
\setslot{hungarumlaut}
  \Unicode{030B}{COMBINING DOUBLE ACUTE ACCENT}
  \comment{The long Hungarian umlaut `\H{}'.}
\endsetslot

\Fi

\begincomment
\subsection{Symbols}
\endcomment

\ifnumber{\int{ligaturing}}<{2}\then

\nextslot{11}
\setslot{arrowup}
  \Unicode{2191}{UPWARDS ARROW}
\endsetslot

\setslot{arrowdown}
  \Unicode{2193}{DOWNWARDS ARROW}
\endsetslot

\setslot{quotesingle}
  \Unicode{0027}{APOSTROPHE}
\endsetslot

\setslot{exclamdown}
  \Unicode{00A1}{INVERTED EXCLAMATION MARK}
\endsetslot

\setslot{questiondown}
  \Unicode{00BF}{INVERTED QUESTION MARK}
\endsetslot

\Fi

\nextslot{32}
\ifnumber{\int{ligaturing}}>{0}\then

\setslot{lslashslash}
  \comment{When this character is followed by 
     \textunicode{004C}{LATIN CAPITAL LETTER L} then the combined 
     result is \textunicode{0141}{LATIN CAPITAL LETTER L WITH STROKE}; 
     this is used by the \cs{L} command. When this character is 
     followed by \textunicode{006C}{LATIN SMALL LETTER L} then the 
     combined result is \textunicode{0142}{LATIN SMALL LETTER L WITH 
     STROKE}; this is used by the \cs{l} command. There are no further  
     semantics for this character.}
  \ligature{LIG}{L}{Lslash}
  \ligature{LIG}{l}{lslash}
  \comment{These ligatures, and the characters they point to, were 
     added by Alan Jeffrey early in \textsf{fontinst} development in 
     order to allow the character in this slot to exhibit the correct 
     behaviour even in fonts where there is no corresponding glyph.}
\endsetslot

\Else

\setslot{visiblespace}
  \Unicode{2423}{OPEN BOX}
  \comment{A visible space glyph `\textvisiblespace'.}
\endsetslot

\Fi


\nextslot{34}
\ifnumber{\int{ligaturing}}>{0}\then

\setslot{quotedblright}
  \Unicode{201D}{RIGHT DOUBLE QUOTATION MARK}
\endsetslot

\Else

\setslot{quotedbl}
  \Unicode{0022}{QUOTATION MARK}
\endsetslot

\Fi

\nextslot{60}
\ifnumber{\int{ligaturing}}={2}\then

\setslot{exclamdown}
  \Unicode{00A1}{INVERTED EXCLAMATION MARK}
\endsetslot

\skipslots{1}

\setslot{questiondown}
  \Unicode{00BF}{INVERTED QUESTION MARK}
\endsetslot

\Else

\setslot{less}
  \Unicode{003C}{LESS-THAN SIGN}
\endsetslot

\skipslots{1}

\setslot{greater}
  \Unicode{003E}{GREATER-THAN SIGN}
\endsetslot

\Fi

\nextslot{92}
\ifnumber{\int{ligaturing}}>{0}\then

\setslot{quotedblleft}
  \Unicode{201C}{LEFT DOUBLE QUOTATION MARK}
\endsetslot

\Else

\setslot{backslash}
  \Unicode{005C}{REVERSE SOLIDUS}
\endsetslot

\nextslot{95}
\setslot{underscore}
  \Unicode{005F}{LOW LINE}
  \label{underscore}
\endsetslot

\begincomment
\par\medskip
Note that the \(\mathit{ligaturing} > 0\) assignment to 
slot~\ref{dotaccent} is mandatory, not ordinary.
\endcomment

\Fi


\nextslot{123}
\ifnumber{\int{ligaturing}}>{0}\then

\setslot{endash}
  \Unicode{2013}{EN DASH}
  \Ligature{LIG}{hyphen}{emdash}
\endsetslot

\setslot{emdash}
  \Unicode{2014}{EM DASH}
  \comment{In a monowidth font this character is preferably given the 
     width of two normal characters.}
\endsetslot

\Else

\setslot{braceleft}
  \Unicode{007B}{LEFT CURLY BRACKET}
\endsetslot

\setslot{bar}
  \Unicode{007C}{VERTICAL LINE}
\endsetslot

\setslot{braceright}
  \Unicode{007D}{RIGHT CURLY BRACKET}
\endsetslot

\Fi


\begincomment
\section{Fontdimens}
\endcomment

\setfontdimen{1}{italicslant}    % italic slant
\setfontdimen{2}{interword}      % interword space
\setfontdimen{3}{stretchword}    % interword stretch
\setfontdimen{4}{shrinkword}     % interword shrink
\setfontdimen{5}{xheight}        % x-height
\setfontdimen{6}{quad}           % quad
\setfontdimen{7}{extraspace}     % extra space after .


\begincomment
\section{Coding scheme}
\endcomment

\ifnumber{\int{ligaturing}}={2}\then

\setstr{codingscheme}{TEX TEXT}

\Else\ifnumber{\int{ligaturing}}={1}\then

\setstr{codingscheme}{TEX TEXT WITHOUT F-LIGATURES}

\Else

\setstr{codingscheme}{TEX TYPEWRITER TEXT}

\Fi\Fi


\endencoding


\section{Discussion}


\subsection{\texttt{OT1} as math font encoding}

As source for the math requirements on the \texttt{OT1} encoding 
was used the standard \LaTeX\ math set-up~\cite{fontdef}. Those 
definitions that make use of \texttt{OT1} fonts either use the 
\texttt{operators} symbol font\slash font family~0 or have math 
class~7 (\cs{mathalpha}).

There are two slots used for math that have different assignments 
in different encoding variants. Slot 36 (\texttt{dollar}\slash 
\texttt{sterling}) depends on the $\mathit{italicizing}$, and is used 
by the commands \cs{mathdollar} (called by \verb|\$|) and 
\cs{mathsterling} (called by \cs{pounds}). This works because these 
commands explicitly take the character from a font with the correct 
$\mathit{italicizing}$.

Slot~95 (\texttt{dotaccent}\slash \texttt{underline}) depends on the 
$\mathit{ligaturing}$ and is used by the \cs{dot} command. This 
command does \emph{not} work for fonts with \(\mathit{ligaturing}=0\), 
and hence e.g.\ the formula \verb|$\mathtt{\dot{x}}$| does not produce 
a typewriter dotted `x', but rather an `x' and underscore printed on 
top of each other. This is thus an error, but due to that it is 
unlikely that the error will be missed by the author who encounters 
it, the error is probably harmless.


\subsection{\texttt{OT1} as text font encoding}

The sources used to determine the text requirements on the 
\texttt{OT1} encoding were~\cite{ltoutenc}.

It turns out that there are LICR commands which rely on non-mandatory 
features of the font. It is mostly for the \(\mathit{ligaturing} = 0\) 
fonts that commands produce incorrect results. The following commands 
work with all \texttt{OT1} fonts which have \(\mathit{ligaturing} > 0\) 
but fail with the others: \cs{L}, \cs{l}, \cs{.}, \cs{H}, 
\cs{textemdash}, \cs{textendash}, and \cs{textquotedblleft}.
In addition, the command \cs{textquotedblright} produces a 
reasonable, but not exactly correct, result.

Traditionally the \cs{textexclamdown} and \cs{textquestiondown} have 
only worked for fonts which have \(\mathit{ligaturing} = 2\), but 
that can be fixed; see~\cite{latex/3368}.



\begin{thebibliography}{9}
\bibitem{ltoutenc}
  Johannes Braams, David Carlisle, Alan Jeffrey, Frank Mittelbach, 
  Chris Rowley, and Rainer Sch\"opf:
  \textit{ltoutenc.dtx}, v\,1.91 (2000);
  the file \texttt{ltoutenc.dtx} in the \LaTeX\ base distribution. 
\bibitem{latex/3368}
  Lars Hellstr\"om:
  \textit{\texttt{OT1} def.\ of \cs{textexclamdown} and 
  \cs{textquestiondown}}, \LaTeX\ bugs database entry 
  \textbf{latex/3368}, 2001.
%   ; \textsc{http:}/\slash \texttt{www.latex-project.org}\slash
%   \texttt{cgi-bin}\slash \texttt{ltxbugs2html\discretionary{?}{}{?}%
%   pr=latex/3368}.
\bibitem{ComputerModern}
  Donald E. Knuth:
  \textit{Computer Modern Typefaces}, 
  volume E of \textit{Computers \& Typesetting},
  Ad\-di\-son--Wes\-ley, 1986, xvi+588\,pp.;
  ISBN~0-201-13446-2.
\bibitem{fontdef}
  Frank Mittelbach and Rainer Sch\"opf:
  \textit{The \texttt{fontdef.dtx} file}, v\,2.2x (1999);
  the file \texttt{fontdef.dtx} in the \LaTeX\ base distribution. 
\end{thebibliography}


\end{document}



