\def\fileversion{0.01}
\def\filedate{91/8/20}
\def\docdate {91/8/20}

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%
%
%\iffalse   % This is a META comment
%
% File `plainfsl.doc'.
% Copyright (C) 1991 Wayne G. Sullivan, all rights reserved.
%
% Copying of this file is authorized only if either
% (1) you make absolutely no changes to your copy, or
% (2) you use a different name for your modified file.
%
%
% Error reports (unmodified files only):
%                          Department of Mathematics
%                          University College
%                          Dublin 4, Ireland
%                 Bitnet:  <WSULIVAN@IRLEARN>
%
%
%\fi
%
%
% \title{The file {\tt plainfsl.doc}\thanks{This file has version
%        number \fileversion, dated \filedate.  The documentation was
%        last updated on \docdate.}.}
%
% \author{Wayne G. Sullivan}
%
% \maketitle
%
% \StopEventually{}
%
% \section{Font selection scheme}
% The Mittelbach\slash Sch\"opf font selection scheme is a systematic
% approach for handling of fonts in \TeX\ documents. It was originally
% designed for use under \LaTeX, but it may be used with other formats.
% The purpose of the present work is to provide the necessary adaptations
% for \PlainTeX\null. First we include a few macros based on those in
% \LaTeX\null.
% \begin{macro}{\protect}
% \begin{macro}{\makeatletter}
% \begin{macro}{\makeatother}
% The control sequence \verb+\protect+ is rather subtle. In ordinary text
% setting it is superfluous. However, there are numerous contexts where
% it can be used to control the way macros are expanded, as in the
% \verb+\typeout+ macro given below. Other contexts require other tricks.
% Some macros of \PlainTeX use {\tt @} as a letter to inhibit
% redefinition. To access these, the catcode of {\tt @} needs to be
% changed. The experienced \TeX\ user may occasionally wish to access
% these {\em private\/} macros, so the required catcode changes are
% assigned to control sequences. We use such a change here.
%    \begin{macrocode}
\let\protect\relax
\def\makeatletter{\catcode`\@11 }
\def\makeatother{\catcode`\@12 }
\makeatletter
%    \end{macrocode}%
% \end{macro}
% \end{macro}
% \end{macro}
% \begin{macro}{\@ifundefined}
% \begin{macro}{\@ifdefinable}
% \LaTeX~is sometimes careful about assigning new macro names. In these
% cases the new identifier will be checked to see if it has already been
% used. \verb+\@ifundefined+ takes the characters in the identifier
% as its first parameter and uses \verb+\csname+ to construct the
% control sequence name. Control sequences so constructed are given
% the value \verb+\relax+ if they have not previously appeared.
% If the control sequence defined by the characters has not previoulsy
% appeared, or is currently equivalent to \verb+\relax+, then the
% second parameter of \verb+\@ifundefined+ is included; otherwise the
% third. The macro \verb+\@ifdefinable+ takes as first parameter a
% control sequence which is converted to its characters. If these
% characters form an undefined control sequence (in the above
% sense), then the second parameter of the macro is included.
% Otherwise an error messsage is issued.
%    \begin{macrocode}
\long\def\@ifundefined#1#2#3{\expandafter\ifx\csname
    #1\endcsname\relax#2\else#3\fi}
\long\def\@ifdefinable#1#2{\relax\count@\escapechar\escapechar\m@ne
    \edef\@tempa{\string#1}\escapechar\count@
    \expandafter\@ifundefined\expandafter{\@tempa
    }{#2}{\errmessage{\string#1 already defined}}}
%    \end{macrocode}%
% \end{macro}
% \end{macro}
% \begin{macro}{\typeout}
% \begin{macro}{\@latexerr}
% \begin{macro}{\@eha}
% One of the main tools the font selection scheme uses for sending
% messages to the screen is \verb+\typeout+. Without the
% redefinition of \verb+\protect+, the output in some cases would
% be considerably less legible. For reporting errors the font
% selection scheme uses \LaTeX\ macros which are given here.
% The \verb+\@eha+ error help given here is even more terse
% than the original: such general messages are of little use
% anyway.
%    \begin{macrocode}
\def\typeout#1{{\let\protect\string\immediate\write\sixt@@n{#1}}}
\def\@eha{Enter `?' for options.}
\def\@latexerr#1#2{%
\edef\@tempc{#2}\expandafter\errhelp\expandafter{\@tempc}%
   \errmessage{#1}}
%    \end{macrocode}%
% \end{macro}
% \end{macro}
% \end{macro}
% \begin{macro}{\mbox}
% Most of those who use \TeX\ are sometimes baffled by \TeX's mode
% (or mood). In order to get a paragraph to start with an \verb+\hbox+
% some coaxing must be employed. \verb+\leavevmode+ does the trick and
% leaves no sticky residue.
%    \begin{macrocode}
\def\mbox#1{\leavevmode\hbox{#1}}
%    \end{macrocode}%
% \end{macro}
% \begin{macro}{\@ifnextchar}
% \begin{macro}{\@ifstar}
% It is convenient when writing macros to have a technique for
% modifying the interpretation based on the first character
% following the control sequence. Thus \verb+\@ifstar+ will
% invoke one set of instuctions if the character following is
% {\tt *} and another otherwise. This is achieved by means of
% the \TeX\ primitive \verb+\futurelet+. The matter is
% complicated by the fact that spaces are skipped when
% undelimited macro parameters are scanned. So if
% \verb+\futurelet+ detects a space, the macro should skip on until
% a non-blank token is found. The coding borders on the clever,
% but because of the subtle difference between characters and
% control sequences equating to characters, the whole business
% could be derailed by a devious or unlucky token. Below, to obtain
% space tokens in the desired locations, \verb+\edef+ and
% \verb+\expandafter+ are used. The macros so defined do not
% contain \verb+\expandafter+.
%    \begin{macrocode}
\edef\@ifnextchar#1#2#3{\let\noexpand\@tempc=#1\def\noexpand
    \@tempa{#2}\def\noexpand\@tempb{#3}\noexpand\@peeknextch\space}
\expandafter\def\expandafter\@peeknextch\space
      {\futurelet\@tempd\@finifnextch}
\expandafter\def\expandafter\@finifnextch
\expandafter{\expandafter\ifx\space\@tempd\let\@tempd\@peeknextch\else
    \ifx\@tempd\@tempc\let\@tempd\@tempa\else\let\@tempd\@tempb\fi\fi
    \@tempd}
\def\@ifstar#1#2{\@ifnextchar*{\def\@tempa*{#1}\@tempa}{#2}}
%    \end{macrocode}
% This completes the discussion of the macros adapted from \LaTeX.
% \end{macro}
% \end{macro}
% \section{Plain fonts}
% Next we proceed to the font selection macros which are described
% in detail in their own documentation. Since these will be loaded
% after \PlainTeX, some font material is already loaded. If your
% version of plain preloads more than the 16 basic fonts and you
% make little use of the other preloaded fonts, you might consider
% commenting out the extra preloaded fonts in {\tt plain.tex}. Now that
% there is a much greater choice of fonts for use with \TeX,
% it makes even more sense to preload only fonts which are
% frequently used. Whether a font is preloaded does not effect the
% final output. The only advantage of preloading is that it may
% result in slightly reduced processing time. Excessive preloading
% can result in reduced processing speed.
% The font selection scheme does its own
% allocation of math alphabets, {\it i.e.,} \verb+\fam+, so we need to
% reset this allocation to the minimum corresponding to
% roman, math italic, symbol and extensible. We also give
% the font selection name to the extensible font.
%    \begin{macrocode}
\count18=3 % deallocate plain math alphabets=>\fam numbers
\expandafter\let\csname cmex/m/n/10\endcsname=\tenex
%    \end{macrocode}%
% \section{Mittelbach\slash Sch\"opf}
% Next we append the bulk of the font selection macros by using
% the {\em docstrip\/} utility to include the macros in
% the same file as the above macros. However, near the end
% of the scheme there are macros which appeal directly
% to \LaTeX\ structures. We use a trick to omit these. The
% scheme requests the file {\tt xxxlfont.sty} to give the user
% the option of retaining the basic way that \LaTeX\ handles
% math mode fonts or use a different approach. For use with
% \PlainTeX\ we include a file with the name {\tt xxxlfont.sty},
% which itself will request the input of a file {\tt yyylfont.sty},
% again to allow the user choice of math mode font selection
% styles. Penultimatily {\tt xxxlfont.sty} will request the
% input of a file {\tt anyextra.xyz} to allow the user to include
% other material in the format file. Only one file is requested;
% if the user has several to include, then a single file which
% inputs each of these should be made. If no further material
% is to be included, then the user should enter the name of
% the system {\em null\/} file or make up a file which consists
% simply of \verb+\endinput+. The file {\tt xxxlfont.sty} then
% executes \verb+\dump+.
% \section{Other files needed}
% In addition to {\tt plainfsl.tex} and {\tt xxxlfont.sty} one needs
% a {\tt fontdef.tex}. There are several of these available from the
% general font selection distribution. This file should be adapted to
% local available fonts. Also requested during the format processing
% is {\tt preload.tex}. The user should make up his own preload file
% based on the fonts commonly used, but it is not necessary to preload
% any additional fonts: a system null file (or equivalent)
% can be supplied in place of {\tt preload.tex}. Also needed is either
% {\tt oldlfont.sty} or {\tt basefont.tex}.
% \Finale
%
\endinput