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<meta name="author" content="William F. Hammond" />
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<h1 class="display">The GELLMU Manual</h1>
<h4 class="display">Version 0.8.4 Release, July 2007</h4>
<h2 class="display">William F. Hammond</h2>
<h4 class="display">
Dept. of Mathematics & Statistics University at Albany Albany, New York 12222 (USA)</h4>
Email: <kbd>[email protected]</kbd>
<h4 class="display">Revision of July 5, 2007</h4>
<h5 class="display">Copyright © 2001–2007 William F. Hammond</h5>
<h3 class="display">ABSTRACT</h3>
<blockquote>

This is the manual for Generalized Extensible LaTeX-Like
Markup (GELLMU). The central focus in the GELLMU project is to tie
LaTeX to the worlds of SGML and XML by providing LaTeX-like markup
for writing documents under SGML and XML vocabularies (formally
known as document types). 

The Manual explains the distinction between basic and
advanced use, provides a description of regular
GELLMU as an instance of advanced GELLMU, and discusses
the use of the didactic production system, which is the project's suite of
processors for working with regular GELLMU. 

The Manual also deals with the metacommands available when
writing GELLMU markup. One of these metacommands is the project's
emulation of LaTeX's newcommand, which makes it possible to
have macros taking multiple arguments while writing for an SGML or
XML vocabulary.

</blockquote>
<div class="tableofcontents">
<h3>Table of Contents</h3>
<dl class="tableofcontents">
<dd>1  Introduction... <a href="#SU-1">*</a>
</dd><dd>
2  Basic GELLMU... <a href="#SU-2">*</a>
</dd><dd>
3  Metacommands... <a href="#SU-3">*</a>
<dl><dd>
3.1  \documenttype... <a href="#SU-3.1">*</a>
</dd><dd>
3.2  \newcommand... <a href="#SU-3.2">*</a>
</dd><dd>
3.3  \begin{} … \end{}... <a href="#SU-3.3">*</a>
</dd><dd>
3.4  \macro and \Macro... <a href="#SU-3.4">*</a>
</dd><dd>
3.5  Macro-Level Fronting of SGML Element Names... <a href="#SU-3.5">*</a>
</dd></dl></dd><dd>
4  Advanced GELLMU... <a href="#SU-4">*</a>
<dl><dd>
4.1  Illustrations.... <a href="#SU-4.1">*</a>
</dd><dd>
4.2  Multiple Argument/Option Syntax... <a href="#SU-4.2">*</a>
</dd><dd>
4.3  Limitation in Regard to XML... <a href="#SU-4.3">*</a>
</dd></dl></dd><dd>
5  The Didactic Document Type... <a href="#SU-5">*</a>
<dl><dd>
5.1  Suggestions and Caveats... <a href="#SU-5.1">*</a>
</dd><dd>
5.2  Markup Fundamentals... <a href="#SU-5.2">*</a>
<dl><dd>
5.2.1  Explicitly named commands.... <a href="#SU-5.2.1">*</a>
</dd><dd>
5.2.2  Certain single characters.... <a href="#SU-5.2.2">*</a>
</dd><dd>
5.2.3  Certain strings... <a href="#SU-5.2.3">*</a>
</dd></dl></dd><dd>
5.3  Large Structure... <a href="#SU-5.3">*</a>
</dd><dd>
5.4  Sectioning... <a href="#SU-5.4">*</a>
</dd><dd>
5.5  Labels, References, and Anchors... <a href="#SU-5.5">*</a>
<dl><dd>
5.5.1  Labels and Sequencing... <a href="#SU-5.5.1">*</a>
</dd><dd>
5.5.2  Anchors... <a href="#SU-5.5.2">*</a>
</dd><dd>
5.5.3  Example Emulating a LaTeX Counter... <a href="#SU-5.5.3">*</a>
</dd></dl></dd><dd>
5.6  General Usage for Sectional Units... <a href="#SU-5.6">*</a>
<dl><dd>
5.6.1  The Content Model... <a href="#SU-5.6.1">*</a>
</dd><dd>
5.6.2  The LaTeX-Like Form of General Usage... <a href="#SU-5.6.2">*</a>
</dd></dl></dd><dd>
5.7  verbatim, verblist, and
manmac... <a href="#SU-5.7">*</a>
</dd><dd>
5.8  Accents... <a href="#SU-5.8">*</a>
</dd><dd>
5.9  Tabular Environment Emulation... <a href="#SU-5.9">*</a>
</dd><dd>
5.10  Graphic Inclusions... <a href="#SU-5.10">*</a>
</dd></dl></dd><dd>
6  Mathematics in article... <a href="#SU-6">*</a>
<dl><dd>
6.1  General... <a href="#SU-6.1">*</a>
</dd><dd>
6.2  Assertions... <a href="#SU-6.2">*</a>
<dl><dd>
6.2.1  Examples... <a href="#SU-6.2.1">*</a>
</dd><dd>
6.2.2  Usage for assertion... <a href="#SU-6.2.2">*</a>
</dd></dl></dd><dd>
6.3  Equations and Equation Arrays... <a href="#SU-6.3">*</a>
</dd><dd>
6.4  The \mathsym Metacommand... <a href="#SU-6.4">*</a>
</dd></dl></dd><dd>
7  The Didactic Production System... <a href="#SU-7">*</a>
<dl><dd>
7.1  Permission... <a href="#SU-7.1">*</a>
</dd><dd>
7.2  Materials... <a href="#SU-7.2">*</a>
</dd><dd>
7.3  Other Required Software... <a href="#SU-7.3">*</a>
</dd><dd>
7.4  Using the syntactic translator... <a href="#SU-7.4">*</a>
<dl><dd>
7.4.1  Operation in Batch Mode... <a href="#SU-7.4.1">*</a>
</dd><dd>
7.4.2  Interactive Operation... <a href="#SU-7.4.2">*</a>
</dd><dd>
7.4.3  Interrupting the Syntactic
Translator... <a href="#SU-7.4.3">*</a>
</dd></dl></dd><dd>
7.5  Using the didactic production system... <a href="#SU-7.5">*</a>
<dl><dd>
7.5.1  Staged Design... <a href="#SU-7.5.1">*</a>
</dd><dd>
7.5.2  Default Staging... <a href="#SU-7.5.2">*</a>
</dd><dd>
7.5.3  Parsing with nsgmls... <a href="#SU-7.5.3">*</a>
</dd><dd>
7.5.4  Processing with sgmlspl... <a href="#SU-7.5.4">*</a>
</dd><dd>
7.5.5  Environmental Variables... <a href="#SU-7.5.5">*</a>
</dd></dl></dd></dl></dd><dd>
Appendix A  The GELLMU Archive... <a href="#SU-8">*</a>
</dd><dd>
Appendix B  Release Notes... <a href="#SU-9">*</a>
<dl><dd>
B.1  Comments on the Syntactic Translator... <a href="#SU-9.1">*</a>
</dd><dd>
B.2  Comments on the Didactic Production System... <a href="#SU-9.2">*</a>
<dl><dd>
B.2.1  Internationalization... <a href="#SU-9.2.1">*</a>
</dd><dd>
B.2.2  Document Type Definitions... <a href="#SU-9.2.2">*</a>
</dd><dd>
B.2.3  Translation to XML... <a href="#SU-9.2.3">*</a>
</dd><dd>
B.2.4  Translation to HTML... <a href="#SU-9.2.4">*</a>
</dd><dd>
B.2.5  Translation to LaTeX... <a href="#SU-9.2.5">*</a>
</dd><dd>
B.2.6  Future Plans... <a href="#SU-9.2.6">*</a>
</dd></dl></dd></dl></dd></dl>
</div>

<div class="section">
<h3>1.  <a id="SU-1"></a><a id="intro"></a>Introduction</h3>

GELLMU is an acronym for “Generalized Extensible
LaTeX-Like MarkUp”, which is the author's concept for using LaTeX-like
markup to write consciously for SGML document types such as HTML,
DocBook, TEI, or GELLMU's own didactic LaTeX-like document
type called article. 

It evolved from earlier thought about delineation of a coherent subset
of LaTeX commands with the property that if a LaTeX document used
only those commands then it could be translated with full reliability
to other formats including HTML so that documents could be prepared
both for print and for the web from a single source. 

Problems with this early thought during the years 1996–1997 included
the fact that there did not seem to be a community of LaTeX users
willing to focus on a narrow vocabulary and the fact then of a legacy
practice that mixed LaTeX commands freely with non-LaTeX TeX
commands. 

The present idea was crystalized in the summer of 1998 while the author
was looking at Ulrich Vieth's LaTeX markup for the TeX Directory
System (TDS) specification from the TeX User Group
(TUG), which now is physically realized in TUG's
TeXLive series of TeX-related software distributions on
CDrom. The HTML version of that specification was derived
through an intermediate ad hoc translation from LaTeX to
Texinfo, the language of the GNU Documentation System,
which is a robust hypertex system pre-dating HTML driven by TeX
the Program. 

In thinking about generalizing Vieth's ad hoc translation, which used
GNU Emacs Lisp (Elisp), one of the most widely available
<a href="http://www.gnu.org/">free</a> cross-platform programming languages
for which there is a free robust engine, the same engine that
underlies the interactive editing interface of Emacs, the author
realized that the structure of Texinfo is very much like that of an
authoring level SGML document type. From that idea it was a small
step to decide that one might profitably write Elisp code to use LaTeX-like
markup for the conscious writing of a new LaTeX-like article document
type. 

The idea, which by itself saves keystrokes, gains significant power
with the emulation of LaTeX's newcommand. Although SGML
markup offers both subdocument inclusions and macro substitutions
using the notion of entity, there is no SGML-standard macro
facility that takes arguments. Moreover, GELLMU's newcommand,
which is, unlike LaTeX's, a simple macro substitution facility,
also provides a base for experimenting with document type extensions
in a way that the SGML notion of entity does not since SGML
entities are invoked with a notation that is apart from that used to
markup with SGML elements, which are the objects corresponding
in the GELLMU scheme with LaTeX-like commands. 

Software associated with the GELLMU project falls into two parts:

<ol class="decimal">
<li> The syntactic translator. This is a purely syntactic layer for converting
LaTeX-like markup in configurable ways to SGML markup. Its output may
be handled in standard SGML or XML systems. 
</li>
<li> The didactic production system. This component is a sketch, which might usefully
serve as a base for further development, of an SGML production
system for an authoring environment that consists of

<ol class="lower-alpha">
<li> An SGML document type called article that is
accompanied by a corresponding XML document type.

</li>
<li> A package of extensible translating utilities written
in the language Perl.

</li>
</ol>

As its name suggests, these materials are didactic and
should be regarded as unfinished for production work. </li>
</ol>


There are two overall concepts: basic mode and advanced
mode. The basic mode may be used to write consciously for any
standard document type such as HTML, DocBook, or TEI,
and the syntactic translator is for that mode the only software under this project that
might be relevant. The advanced mode incorporates a configurable
broader array of LaTeX-like markup features, mostly for brevity, in the syntactic translator.
This mode is fully developed only for use with a LaTeX-like document type
such as the didactic article document type that is part of the
didactic production system. 

One may use any SGML or XML processing framework in working
with the article document type. The didactic production system includes what is
needed to produce both HTML and regular LaTeX forms of an
article instance. Consequently, one is able to produce both
DVI using the LaTeX format for TeX, the program, and PDF
using the LaTeX format for PDFTeX, the program. Moreover, one
may tune the PDF in various ways using small alterations of the
Perl code for translating the XML version of article
to regular LaTeX.

</div>

<div class="section">
<h3>2.  <a id="SU-2"></a><a id="basic"></a>Basic GELLMU</h3>

Neither the basic nor the advanced mode involves in any way adoption
of the language of LaTeX. (But many command names under the didactic
article document type, mimic LaTeX command names.) There are
two fundamental ideas:

<ol class="decimal">
<li> A LaTeX-like command “<kbd>\foo</kbd>” corresponds
to an SGML element “<kbd><foo></kbd>”. 
</li>
<li> The syntactic translator is almost entirely ignorant of vocabulary
and a name like foo need not have meaning in it although
it must have meaning in the document type for which one is
consciously writing.<a id="revfnote1" href="#fnote1">1</a>
</li>
</ol>

To use the basic mode one must be familiar with the SGML document
type for which one is writing. Ordinary HTML is an example. Very
few of the features in the advanced markup not also part of the basic
markup<a id="revfnote2" href="#fnote2">2</a>
make any sense for use in the direct preparation of HTML with LaTeX-like
input. 

GELLMU uses LaTeX special characters such as ‘<kbd>\</kbd>’,
‘<kbd>{</kbd>’, and ‘<kbd>}</kbd>’ along with LaTeX-like argument/option syntax,
where braces immediately following a command name indicate command
arguments and square brackets, i.e., ‘<kbd>[</kbd>’ and
‘<kbd>]</kbd>’, indicate command options. A command corresponds to
an SGML element, and in basic mode a command may have at most one
argument, the content of which corresponds to SGML element content,
and at most one option, the content of which corresponds to a list of
SGML attribute specifications. Thus for example, in basic mode for
HTML one may use the markup

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\a[href="http://www.w3.org/"]{The World Wide Web Consortium}</kbd></td></tr></tbody></table></div>

to form the HTML anchor:

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd><a href="http://www.w3.org/">The World Wide Web Consortium</a></kbd>
</td></tr></tbody></table></div>

(The formation of anchors with the didactic article document
type in advanced mode is slightly more complicated because the
characters ‘<kbd>=</kbd>’ and ‘<kbd>/</kbd>’, which may acquire special (and
“overloaded”) semantic significance in mathematical
contexts, are held for delayed evaluation as empty elements and
because the syntactic translator, which does not recognize command names, regards this
usage in advanced mode as multiple
<a href="#argopt">argument/option syntax</a> (section 4.2), which is not part of basic
mode.)

An example of the distinction between basic and advanced GELLMU is that
in advanced mode it is possible and easy to arrange to have a blank line,
as in LaTeX, represent the beginning of a paragraph. In basic mode
for HTML one
must<a id="revfnote3" href="#fnote3">3</a>
use “<kbd>\p</kbd>” to begin a paragraph, and for the XML version of
HTML one must also provide markup for the end of every paragraph, which
may be done in several ways. 

For some of the details on using the basic markup with HTML see
<a href="ghtml.html">Using the GELLMU Syntactic Translator to Write HTML</a>.
It will be instructive to have the parallel <a href="ghtml.glm">source
markup</a> available at the same time.

</div>

<div class="section">
<h3>3.  <a id="SU-3"></a><a id="meta"></a>Metacommands</h3>

A metacommand is a LaTeX-like command that does not correspond to an
SGML element. Each metacommand is handled internally by the
syntactic translator.


<div class="subsection">
<h4>3.1.  <a id="SU-3.1"></a><a id="doctype"></a>\documenttype</h4>

A document prepared in GELLMU source usually begins with a
documenttype command. For example,

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\documenttype{html}</kbd></td></tr></tbody></table></div>

is used to begin a document prepared for the most common form
of classical HTML. 

The syntactic translator has two public variables
gellmu-doctype-keylist and gellmu-doctype-info,
which are Elisp associative lists, that enable one to match XML
or SGML “<kbd><!DOCTYPE ... ></kbd>” declarations with
LaTeX-like

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\documenttype[</kbd>my-optional-key<kbd>]{</kbd>my-doctype<kbd>}</kbd></td></tr></tbody></table></div>

commands, where my-optional-key is available to override a
default key for my-doctype. Thus, for example,
“<kbd>\documenttype{html}</kbd>” points to the default key for
“<kbd>html</kbd>”, which is “<kbd>html-4.01</kbd>” and which points to
the W3C HTML 4.01 Transitional document type, while

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\documenttype[xhtml-1.0s]{html}</kbd></td></tr></tbody></table></div>

indicates W3C XHTML 1.0 Strict. 

A user may configure these variables without modifying the source
code for the GELLMU syntactic translator, but minimal knowledge of Elisp will
be required. A future release might provide a configuration file
for this purpose. 

A second option for the documenttype metacommand, which must
follow the single required argument, is provided for writing an
internal declaration subset. The contents of an internal declaration
subset constructed this way may be any internal declaration subset
material. However, some care is required for entering characters
that are special. To ease the handling of special characters four
metacommands have been provided for use inside the internal declaration
subset:

<dl>
<dd> <kbd>\attlist{...}</kbd></dd>
<dd> <kbd>\element{...}</kbd></dd>
<dd> <kbd>\entity{...}</kbd></dd>
<dd> <kbd>\notation{...}</kbd></dd>
</dl>

For example, a user who wishes to be able in source to use
“<kbd>&quo;</kbd>” to reference the ASCII quotation mark
when writing consciously in basic mode for TEI.2 would begin
the source file with:

<dl class="verblist">
<dd><kbd>
\documenttype{TEI.2}[</kbd></dd>
<dd><kbd>
\entity{quo "&#x22;"}</kbd></dd>
<dd><kbd>
]</kbd></dd>
</dl>


</div>

<div class="subsection">
<h4>3.2.  <a id="SU-3.2"></a><a id="newcommand"></a>\newcommand</h4>

From a user's viewpoint this provides emulation of LaTeX's
newcommand. But it is a simple facility providing macro
substitution with arguments forward in a source file from the
point of its occurrence. It differs from the newcommand
facility in LaTeX in that it does not add the name
of a newcommand to any namespace. Instead, as the syntactic translator encounters
each newcommand definition, it performs the corresponding expansions
and then forgets the name.<a id="revfnote4" href="#fnote4">4</a>

The general construction of a newcommand definition is

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\newcommand{</kbd>name<kbd>}[</kbd>nargs<kbd>][</kbd>first<kbd>]{</kbd>value<kbd>}</kbd></td></tr></tbody></table></div>

where name is the name of the newcommand,
nargs optionally specifies the number of its arguments,
first is an optionally-provided default value for the first
argument, and value denotes the value string. 

In the value string the character ‘<kbd>#</kbd>’ is used to reference an
argument by the numeric value of its position. Thus, “<kbd>#1</kbd>”
refers to the first argument that is provided at an invocation of
the newcommand, “<kbd>#2</kbd>” the second, etc., and there is no limit
on the number of arguments. It is not required that nargs be
supplied in order to define and use a newcommand taking
arguments. However, for the sake of automatic error checking the
use of nargs is strongly recommended when the definition of
a newcommand taking arguments is entered. 

Example. In writing HTML one might use

<dl class="verblist">
<dd><kbd>
\newcommand{\href}[2][http://www.w3.org/]{\a[href="#1"]{#2}}</kbd></dd>
</dl>

for brevity in writing many HTML anchors. With this definition the
invocation

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\href{http://www.myweb.mydomain/me.html}{my web page}</kbd></td></tr></tbody></table></div>
 gives
rise to the HTML markup

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd><a href="http://www.myweb.mydomain/me.html">my web page</a></kbd></td></tr></tbody></table></div>

while the invocation
“<kbd>\href{Web Central}</kbd>” gives rise to

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd><a href="http://www.w3.org/">Web Central</a></kbd> . </td></tr></tbody></table></div>


Rules.

<ol class="decimal">
<li> The name of a newcommand may not be referenced in its
value string.<a id="revfnote5" href="#fnote5">5</a>

</li>
<li> A newcommand may not be invoked before it is defined unless
the invocation occurs in the value string of another newcommand
definition in which case the definition of the latter may be first and
must be first if the invocation of the former in the definition
of the latter involves argument substitutions. 
</li>
</ol>


Failure to observe these rules may cause the syntactic translator to enter an infinite
recursive loop. If a user suspects this may have happened, then the
invocation of the syntactic translator should be <a href="#interrupt">interrupted</a> (section 7.4.3).

</div>

<div class="subsection">
<h4>3.3.  <a id="SU-3.3"></a><a id="beginend"></a>\begin{} … \end{}</h4>

These provide emulation of LaTeX environment notation without
actually providing anything that is not otherwise available. Markup
which resembles that for a LaTeX environment simply resolves to an
SGML element. This usage may be convenient for SGML elements of
large scope such as, for example, the body of an HTML
document. 

With advanced mode the special form

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\begin{document} . . . \end{document}</kbd></td></tr></tbody></table></div>

may be used to emulate the corresponding feature of LaTeX for a
document type, such as the didactic article document type,
that in the large consists of a preamble and a body.

</div>

<div class="subsection">
<h4>3.4.  <a id="SU-3.4"></a><a id="macmac"></a>\macro and \Macro</h4>

Use of these is discouraged in the absence of a need. One situation
that presents a need is name “fronting”: see the
discussion below in <a href="#fronting">section 3.5</a>.
Please note that in most situations one may use newcommand
without an argument for simple macro substitutions. 

macro and Macro do very much the same thing except
for the order of expansions. Every macro is expanded forward
as encountered before any newcommand definition is expanded. Every
Macro is expanded forward after every newcommand
has been expanded. 

There are four primary differences between macro and Macro,
on the one hand, and newcommand, on the other hand.

<ol class="decimal">
<li> Neither macro nor Macro can be used to define a
macro that takes arguments. 
</li>
<li> The name of a newcommand must consist of word characters,
but there is no restriction on the characters, apart from unbalanced
brace characters (‘<kbd>{</kbd>’ and ‘<kbd>}</kbd>’), that may appear in
the name field of a macro or Macro metacommand. 
</li>
<li> If the name of a macro or Macro does not begin
with the command sequence introducer, i.e., the character ‘<kbd>\</kbd>’,
then an invocation of that metacommand is given by every forward match
of its name. The use of such names is strongly discouraged because
document segments can then become opaque much too easily. 
</li>
<li> A newcommand invocation, absent the use of a semi-colon
for termination, is only effective at the whole word level — with
word here denoting a maximal string of successive word
characters — whereas macro and Macro invocations are
effective regardless of word boundaries. 
</li>
</ol>


Elaboration on the last point: If <kbd>x</kbd> is the name of a
newcommand, then invocations are
only considered by the syntactic translator on the string “<kbd>\x</kbd>” when it is followed
by a non-word character. For example, if the locale is us-ascii,
then the word characters are the 52 upper and lower case letters
and the ten numerals. Therefore with newcommand, as with its
namesake in regular LaTeX, the use of “x” as a name will
not intercept the occasions of “<kbd>\x</kbd>” as an initial
substring of “<kbd>\xy</kbd>”. With either macro or
Macro such interception does take place. One may block it at
the point of an invocation with the markup “<kbd>\x;</kbd>”, and when
this is done, the terminating semi-colon is removed. 

Human authors using either macro or Macro may find
unanticipated interactions between the three forms of macro
substitution. 

Unbalanced brace characters, i.e., the characters ‘<kbd>{</kbd>’ and
‘<kbd>}</kbd>’, may not be used in the name field or the value field of
any form of macro metacommand.

</div>

<div class="subsection">
<h4>3.5.  <a id="SU-3.5"></a><a id="fronting"></a>Macro-Level Fronting of SGML Element Names</h4>

The word fronting as used here describes the practice of
modifying the meaning of an SGML element name by using one or
more of the macro facilities to generate usage of the same name as
an element combined with other markup using the syntax that would
otherwise correspond to basic use of the element. 

Suppose, for example, one wants all paragraphs in HTML (marked
with <kbd>\p</kbd> in GELLMU source) to be placed in a (style) class called
custom. 

Recommended procedure: Create a new unique name and then use
macro to front it.

<dl class="verblist">
<dd><kbd>
\newcommand{\cp}[1][]{\p[class="custom"]{#1}}</kbd></dd>
<dd><kbd>
\macro{\p}{\cp}</kbd></dd>
</dl>

Each invocation of “<kbd>\p{...}</kbd>” will first be replaced by “<kbd>\cp{...}</kbd>”
because all macro definitions are expanded before any
newcommand definition is expanded. Subsequent expansion
of the newcommand will yield

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\p[class="custom"]{...}</kbd> . </td></tr></tbody></table></div>


This will not intercept the alternate, otherwise nearly equivalent,
markup given with <kbd>\begin{p}</kbd> … <kbd>\end{p}</kbd> since newcommand
is based on simple macro substitution and does not operate at the
level of namespaces.

</div>
</div>

<div class="section">
<h3>4.  <a id="SU-4"></a><a id="advanced"></a>Advanced GELLMU</h3>

The idea with advanced GELLMU is that for SGML document
types sharing structural characteristics with LaTeX one might
wish to have the syntactic translator provide LaTeX-like markup syntax beyond the level
used with basic GELLMU and that these additional layers of syntax
should be configurable. The only substantial realization of this
program so far is the case of the GELLMU didactic document type called article.
The specifics of that realization are discussed in the following
section.


<div class="subsection">
<h4>4.1.  <a id="SU-4.1"></a><a id="illustrations"></a>Illustrations.</h4>

One might want to be able to use blank lines, as in
LaTeX, for introducing new paragraphs in a document type that
provides paragraphs. 

In some article-level document types each sectional unit has a unit
header providing markup for various, often optional, unit descriptors.
It is convenient to be able to use LaTeX-like multiple
<a href="#argopt">argument/option syntax</a> (section 4.2) for these. 

If the document type provides authoring-level mathematical markup
beyond inclusions of the World Wide Web Consortium's
<a href="http://www.w3.org/Math/">Mathematical Markup Language</a> (MathML)
under its <a href="http://www.w3.org/TR/REC-xml-names">XML namespace</a>
regime, then one might want to be able to use the ‘<kbd>$</kbd>’ character
to toggle in and out of inline math, and if the document provides
for math displays, then one might want to use, as in LaTeX, the
strings “<kbd>\[</kbd>” and “<kbd>\]</kbd>” as delimiters for
unstructured mathematical displays, and markup such as

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\begin{equation} . . . \end{equation}</kbd></td></tr></tbody></table></div>

for a single equation, and markup such as

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\begin{eqnarray} . . . \end{eqnarray}</kbd></td></tr></tbody></table></div>

for a list of equations. 

It is important to emphasize, however, that by overall system design
the syntactic translator operates without substantial knowledge of vocabulary. While
it is true that if ‘<kbd>$</kbd>’ is to provide a toggle for an inline
element containing math, say, tmath, then the syntactic translator needs to have
that association made, but the association is provided as the
value of a configuration variable in the syntactic translator that can be changed
between documents so that the syntactic translator may be used with many document
types. 

One way to make such configuration convenient is to use an array of
Elisp functions that are fronts with various variable configuration
packages for the basic function gellmu-trans in the syntactic translator.


The general outline for advanced GELLMU with arbitrary document types
is not fully developed in the present release. Instead the project
has concentrated on the realization of these ideas for the project's
didactic article document type, which is the subject of the
next section. 

As the syntactic translator stands now, basic mode is characterized in the syntactic translator by the
true setting for its Boolean variable gellmu-straight-sgml,
while the configuration used by default for the didactic document type (which
could be handled in basic mode with more verbose source markup)
has that variable set false and also the variable
gellmu-regular-sgml set false. 

The term <a id="regular"></a>regular GELLMU refers to use of the
syntactic translator with the default configuration for the didactic document type. It involves nearly
maximal emulation of LaTeX-like markup; it implies both advanced mode
and the <a href="#ddt">didactic document type</a> (section 5) article.

</div>

<div class="subsection">
<h4>4.2.  <a id="SU-4.2"></a><a id="argopt"></a>Multiple Argument/Option Syntax</h4>

An essential point in the present design is that the whole system
is built from components, each of which has its own
function<a id="revfnote6" href="#fnote6">6</a>.
Consistent with this design the syntactic translator operates with knowledge of syntax
but little or no knowledge of language. 

Multiple argument/option syntax has been built into advanced mode as
part of the overall idea of providing, where sensible, LaTeX-like
features in a precise user markup interface for writing in document
types under SGML and XML. 

What are the rules for converting the multiple argument/option syntax
in source markup into SGML? Direct conversion by the syntactic translator of this
type of usage into XML is not available because such conversion
requires some language knowledge and the program does not operate with
knowledge of language at that level<a id="revfnote7" href="#fnote7">7</a>.
One obtains an XML version of a
document in the didactic production system by using a translator with
minimal knowledge of the command vocabulary to create the XML version
from an SGML version that is the immediate output of the syntactic translator. 

In multiple argument/option syntax, which is much like that of
LaTeX, arguments and options follow command names. Arguments are
delimited by braces, i.e., ‘<kbd>{</kbd>’ and ‘<kbd>}</kbd>’ and options
by square brackets, i.e., ‘<kbd>[</kbd>’ and ‘<kbd>]</kbd>’. There
must be no white space between the arguments and options nor between
the command name and the first member of an argument/option sequence. 

Each command with a multiple argument/option sequence is translated to
an open tag whose name is the name of the command. Each argument is
translated to an ag0 element and each option to an op0
element. (Both ag0 and op0 lie in GELLMU's reserved
name space.) There are two exceptional cases.


<ol class="decimal">
<li> The first argument or option is an option inside which the very
first character is a colon, i.e., ‘<kbd>:</kbd>’. This is the method
provided in advanced mode for the direct entry of an SGML attribute
sequence.<a id="revfnote8" href="#fnote8">8</a>
The entire contents of the option string, apart from the
leading ‘<kbd>:</kbd>’, which is discarded, are understood to be a
sequence of SGML attributes for the SGML element whose name is the
name of the command. There is no syntax check of the attribute
contents by the syntactic translator. Such an attribute option is not treated
as an op0 element. In particular, an attribute option is
correctly followed immediately by a semi-colon, i.e., the character
‘<kbd>;</kbd>’, if and only if the corresponding SGML element is a
defined-empty element under the SGML document type. Since SGML
attributes correspond to very little of classical LaTeX<a id="revfnote9" href="#fnote9">9</a>,
attribute options are seldom used<a id="revfnote10" href="#fnote10">10</a>
in the didactic production system. One such use is for the GELLMU equivalent of latex's
equation* and eqnarray* environments, which is marked up
this way:

<dl class="verblist">
<dd><kbd>
\begin{equation}[:nonum="true"]</kbd></dd>
<dd><kbd>
e = mc^2</kbd></dd>
<dd><kbd>
\end{equation}</kbd></dd>
</dl>

to produce:

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block" mode="display"
><mtable><mtr class="labeled"><mtd></mtd><mtd><mrow><mi>e</mi><mo>=</mo><mi>m</mi><msup><mi>c</mi><mn>2</mn></msup
></mrow></mtd></mtr></mtable></math
>
</li>
<li> The first argument is the only argument and there are no options
apart from a possible attribute option. This case, which is extremely
common, is exceptional relative to argument/option handling
since the sole argument simply becomes element content without an
ag0 wrapper.

</li>
</ol>


When a command has a multiple argument/option sequence, the question
arises whether the ag0 and op0 elements that arise from
the arguments and options are the only content of the element
corresponding to the command. The syntax does not provide a way to
determine this. On the other hand, the SGML document type definition
does provide information that indicates whether other content is
possible. It is beyond the scope of the design of the syntactic translator for the
syntactic translator to read a document type definition. The syntactic translator does, however,
have a configurable list variable gellmu-autoclose-list
that contains the names of elements
for which no content beyond the elements arising from arguments and
options is possible. While it is not necessary that every such
command be entered in this list, when such a command not in the list
is not explicitly followed by an element closing command, it is
possible in some instances for an SGML parser to infer incorrectly
the location of end of the element. Thus, the didactic production system provides a
command anch for making anchors. The document type definition
provides for one option, a reference, and one argument, the anchored
text.<a id="revfnote11" href="#fnote11">11</a>
Because the syntactic translator does not consider the document type definition,
if one enters the markup

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\anch[href="http://www.w3.org/"]{W3C} HQ</kbd> ,</td></tr></tbody></table></div>

unless the name anch is in the list<a id="revfnote12" href="#fnote12">12</a>
gellmu-autoclose-list,
an SGML parser will not have reason to close the anch until
it sees the space following the anchored text “W3C”, and so
that space will be considered insignificant white space with the result
that there will be no space between the anchored text and the following
“HQ”.

</div>

<div class="subsection">
<h4>4.3.  <a id="SU-4.3"></a><a id="xmllimit"></a>Limitation in Regard to XML</h4>

A final general comment about advanced mode is that the features it
can provide beyond basic mode when one is writing consciously for an
XML document type are somewhat limited. For example, blank lines
cannot easily be made adequate for paragraph markup with the XML form
of the didactic article document type. Although it is not a
specific limitation for future editions of the syntactic translator, the vision is that
use of advanced mode will be specifically for a somewhat rich SGML
version of a document type.

</div>
</div>

<div class="section">
<h3>5.  <a id="SU-5"></a><a id="ddt"></a>The Didactic Document Type</h3>

The didactic document type is the document type underlying what is called regular
GELLMU. It is the heart of the idea of GELLMU as a bridge for authors
from LaTeX to the world of XML. More specifically, the bridge is
from the world of a LaTeX article to a document type in the
world of XML, also called article, that has a structure and a
vocabulary similar to those of the LaTeX document class.<a id="revfnote13" href="#fnote13">13</a>
The techniques used in the didactic production system are extensible and can be carried over
to other types of documents than articles. It is important to note
that there are many features in regular LaTeX which have no analogue
so far in the development of this project. One might hope to get an
idea of the extent of coverage by reviewing the examples in the
<a href="#archive">project archive</a> (appendix A). 

When an author prepares a document as a LaTeX article, the
document is being marked up as data for a specific typesetting
program: Donald Knuth's program TeX running with the main LaTeX
facilities loaded. 

When an author prepares a document as GELLMU source, the syntactic translator provides
a LaTeX-like markup interface, but its output is not data for a
specific typesetting program. Rather it is data for a broad class of
processors. This means that multiple output formats can be obtained
from a single source without the need for human intervention because
XML provides a framework that makes it relatively easy to create
reliable programs for translation from an XML document type to other
formats. It offers, moreover, the possibility of translation to
future formats free of any need for human intervention once
translators from the original document type to such formats are
written. The small price one pays for this advantage in moving from
LaTeX markup to GELLMU markup is that the author must learn a few
new things.<a id="revfnote14" href="#fnote14">14</a>

There are two formal constructions of the didactic document type. The name of the
document type is article. The first construction is an SGML
version of article that provides features convenient for
authors that are not available under XML. The second is an XML
version. For most non-technical purposes the two constructions should
be regarded as equivalent. 

The SGML construction of an article is derived from GELLMU
source markup for a document by using the syntactic translator. The didactic document
type is accompanied by a translator implemented under the Perl
language framework sgmlspl by David Megginson (see
the release notes in <a href="#release">appendix B</a>
for more information) for converting the SGML version of an
article to the XML version. 

The description in this section of the manual deals primarily with
source level markup for the didactic document type and with how it is handled <a id="revfnote15" href="#fnote15">15</a>
by the time the XML version of an article is generated. Secondarily
there is comment on how it is rendered in the chief output formats
of the didactic production system, which are PDF, classic HTML, and XHTML+MathML. 

A quick glance at the <a href="#flow">flowchart</a> (section 7.5.2) shows that the first
XML stage — author-level XML — may be viewed as a second entry
point to didactic production system processing. Some day this could become a reasonable
formatting route for translations from things like Texinfo,
DocBook, and, even perhaps, classical LaTeX itself via a
processor such as tex4ht.


<div class="subsection">
<h4>5.1.  <a id="SU-5.1"></a><a id="caveat"></a>Suggestions and Caveats</h4>

Although this is the manual for a software release, it is not a book.
A document of book size would be required for a full description of
the didactic production system. 

Much of the markup vocabulary is copied from LaTeX. There are some
instances where there is some deviation from LaTeX usage, and many
of those instances are mentioned here. 

Definitive information about the didactic document type may be derived by consulting the
document type definition. Because the didactic production system is conceived as a base for
future development there are sketches in the document type definition
that are not covered by the didactic processors. For example,
although there is sketched code for the analogues of LaTeX's
paragraph and subparagraph commands, which are sectional
in nature, that is found in the translation from SGML to XML, there is
no sketched code for these elements in the two formatters. 

Another way to obtain information about the didactic production system is by studying
examples including this manual and the examples in the
<a href="#archive">project archive</a> (appendix A).

</div>

<div class="subsection">
<h4>5.2.  <a id="SU-5.2"></a><a id="mufund"></a>Markup Fundamentals</h4>

There are several kinds of commands:


<div class="subsubsection">
<h5>5.2.1.  <a id="SU-5.2.1"></a><a id="explicitnames"></a>Explicitly named commands.</h5>

Apart from macro level
metacommands an explicitly named command begins with a maximal
string introduced by the character ‘<kbd>\</kbd>’ followed by
word characters, including the numerals ‘<kbd>0</kbd>’, ‘<kbd>1</kbd>’,
…, ‘<kbd>9</kbd>’. The notion of word character depends on
one's locale, a concept that is formalized in GNU Emacs. In the
ASCII character set the word characters are the 52 upper and
lower case letters and the 10 numerals. The first numeral, if
any, must not be ‘<kbd>0</kbd>’ since such names are reserved for use by
the syntactic translator. Command names are case sensitive. 

An explicitly named command is a container, corresponding to an
SGML element, if its name is immediately followed, without
intervening white space, by the character ‘<kbd>{</kbd>’. In that case
the delimited zone of containment normally ends with the subsequent
balancing character ‘<kbd>}</kbd>’. (LaTeX-like
<a href="#argopt">multiple argument/option</a> (section 4.2) chains deserve more
discussion; for now it will suffice to point out that the use of the
<kbd>\anch</kbd> command in this document for making “anchors” is an
example, and, of course, LaTeX's <kbd>\frac</kbd> command is another example.
For the present discussion these commands are considered to be
containers.)

An explicitly named command corresponds to an SGML
defined-empty element if its name is immediately followed,
without intervening white space, by the character ‘<kbd>;</kbd>’. 

An explicitly named command corresponds to an SGML element closing
tag if its name is immediately followed, without intervening
white space, by the character ‘<kbd>:</kbd>’. 

The name of an explicitly named command is terminated by a non-word
character. There is a small, possibly acceptable, level of syntactic
ambiguity unless the name terminator is one of ‘<kbd>{</kbd>’,
‘<kbd>;</kbd>’, ‘<kbd>:</kbd>’, or ‘<kbd>[</kbd>’. 

In basic mode if the name terminator is ‘<kbd>[</kbd>’, then that
character introduces a list of SGML attribute specifications, each of
the form name="value", and the list must be
terminated by the character ‘<kbd>]</kbd>’. Then if the following
character is ‘<kbd>{</kbd>’, the named command is a container that ends
with the balancing ‘<kbd>}</kbd>’. Otherwise the following character
may be ‘<kbd>;</kbd>’ if the named command is a defined-empty element and
must be so in that case for direct editing of an XML document type. 

In advanced mode if the name terminator is ‘<kbd>[</kbd>’, then that
character introduces a LaTeX-like command option — part of the
emulation of LaTeX's multiple <a href="#argopt">argument/option syntax</a> (section 4.2)
— unless it is immediately followed, without intervening white space,
by the character ‘<kbd>:</kbd>’, in which case the bracketed content is
a list of SGML attribute specifications. (The initial ‘<kbd>:</kbd>’,
which may be used optionally in basic mode, is discarded.)

In any other case there is some syntactical ambiguity. The syntactic translator will
produce a corresponding SGML open tag unless the logical variable
gellmu-xml-strict has been set.<a id="revfnote16" href="#fnote16">16</a> If
the usage is consistent with the structure of the document type, an
SGML parser will in many cases be able to handle the result
correctly. The result of this type of syntactic ambiguity in source
markup is not tolerated if one is editing directly for an XML document
type. The terminator can be a blank space, but, if so, the
blank space is likely to become invisible after SGML parsing much
in the way that in LaTeX the markup

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\LaTeX document</kbd></td></tr></tbody></table></div>

will be collapsed into the single word form “LaTeXdocument”
when typeset.<a id="revfnote17" href="#fnote17">17</a>

</div>

<div class="subsubsection">
<h5>5.2.2.  <a id="SU-5.2.2"></a><a id="single"></a>Certain single characters.</h5>

The characters
‘<kbd>\</kbd>’, ‘<kbd>{</kbd>’, ‘<kbd>}</kbd>’, ‘<kbd>^</kbd>’,
‘<kbd>_</kbd>’, ‘<kbd>$</kbd>’, ‘<kbd>%</kbd>’, and ‘<kbd>~</kbd>’
have command meanings that are similar to their meanings in LaTeX.
The characters ‘<kbd>;</kbd>’ and ‘<kbd>:</kbd>’ are ordinary characters that
have special meaning at the end of a command name. The character
‘<kbd>#</kbd>’ is also a special character used, as with LaTeX, in
newcommand templates. In source for the didactic
article document type any non-alphanumeric ASCII
character may be escaped (referenced for itself) with a named command,
e.g. ‘<kbd>~</kbd>’ may be referenced for itself as <kbd>\tld;</kbd>. This
is necessary in order to provide delayed evaluation for
ultimate translation to one of many possible ultimate formats. 

The following language meanings apply to both basic and advanced
markup:

<ol class="decimal">
<li> “<kbd>\</kbd>”: Command introducer. Escape in basic mode: <kbd>\\</kbd> . This escape is
incorrect in advanced mode since this notation has a different
meaning — forced linebreak — in LaTeX itself. For the
didactic article
document type the escape is <kbd>\bsl;</kbd> . For other document
types one may resort to an entity reference
if adverse to providing a corresponding
defined-empty element or if one lacks control of the document type.

</li>
<li> “<kbd>{</kbd>”: Command argument opener. Escape: <kbd>\{</kbd> or <kbd>\lbr;</kbd> .

</li>
<li> “<kbd>}</kbd>”: Command argument closer. Escape: <kbd>\}</kbd> or <kbd>\rbr;</kbd> .

</li>
<li> “<kbd>[</kbd>”: Command option opener. Escape: <kbd>\lsb;</kbd> (usually not necessary<a id="revfnote18" href="#fnote18">18</a>).

</li>
<li> “<kbd>]</kbd>”: Command option closer. Escape: <kbd>\rsb;</kbd> .

</li>
<li> “<kbd>;</kbd>”: Command terminator for defined-empty tags. Escape: <kbd>\scl;</kbd> .
Usually an ordinary character.
Its use as a command terminator is invisible and may be
omitted optionally in some contexts. This syntax is analogous to
the use of ‘<kbd>;</kbd>’ as an entity reference terminator in SGML.

</li>
<li> “<kbd>:</kbd>”: Command terminator for close tags. Escape: <kbd>\cln;</kbd> .
Otherwise an ordinary character.
Its use as a command terminator is invisible.

</li>
<li> “<kbd>%</kbd>”: Comment introducer, in force to end of line. Escape: <kbd>\%</kbd> or <kbd>\pct;</kbd> .

</li>
<li> “<kbd>#</kbd>”: Argument marker in newcommand definitions. Escape: <kbd>\#</kbd> or <kbd>\hsh;</kbd> .
In the definition of a newcommand “<kbd>#1</kbd>” indicates the first
invocation argument, “<kbd>#2</kbd>” the second invocation argument, etc.
(There is no limit on the number of arguments.)

</li>
</ol>


The following language meanings apply to advanced markup with
allusion to the didactic article document type.

<ol class="decimal">
<li> “<kbd>~</kbd>”: Non-breaking interword space. Escape: <kbd>\tld;</kbd>.<a id="revfnote19" href="#fnote19">19</a> Equivalent: <kbd>\nbs;</kbd>, cf. <kbd>&nbsp;</kbd> in HTML.

</li>
<li> “<kbd>^</kbd>”: Superscript command. Escape: <kbd>\crt;</kbd> . Equivalent: <kbd>\sup</kbd> or, in math, <kbd>\msup</kbd> .

</li>
<li> “<kbd>_</kbd>”: Subscript command. Escape: <kbd>\_</kbd> or <kbd>\und;</kbd> . Equivalent: <kbd>\sub</kbd> or, in math, <kbd>\msub</kbd> .

</li>
<li> “<kbd>&</kbd>”: Dual use: tabular cells and entity introducer. Escape: <kbd>\&</kbd> or <kbd>\amp;</kbd> . ‘<kbd>&</kbd>’ introduces an entity reference if it is followed
by anything other than white space. It is used, as in LaTeX, as
a tabular cell delineator when it is followed by white space.

</li>
<li> “<kbd>$</kbd>”: Toggle inline math mode. Escape: <kbd>\$</kbd> or <kbd>\dol;</kbd> . Equivalent: “<kbd>\tmath{ . . . }</kbd>”. Nearly equivalent: “<kbd>$ . . . $</kbd>”
or “<kbd>\math{ . . . }</kbd>”.<a id="revfnote20" href="#fnote20">20</a>

</li>
</ol>


</div>

<div class="subsubsection">
<h5>5.2.3.  <a id="SU-5.2.3"></a><a id="certainstrings"></a>Certain strings</h5>

These are strings of plain text with markup significance in the didactic document type that
are part of markup in LaTeX.

<ol class="decimal">
<li> “<kbd>--</kbd>” Short dash as used with a range
of numbers, e.g., 1–2. Equivalent: <kbd>\rdash;</kbd> .

</li>
<li> “<kbd>---</kbd>” Long dash as used for
punctuation, e.g., a dash — like this. Equivalent: <kbd>\pdash;</kbd> .

</li>
<li> “<kbd>\ </kbd>” Blank interword space. Equivalent: <kbd>\spc;</kbd> .

</li>
<li> “<kbd>\,</kbd>” Small horizontal space. Equivalent: <kbd>\hsp;</kbd> .

</li>
<li> “<kbd>\\</kbd>” Forced line break. “<kbd>\\</kbd>” may be used at the end of a line of
input for a forced line break. In a tabular environment
(with the didactic article document type, as in
LaTeX) it begins a new tabular row. Any other use is
deprecated, and will result in translation to the defined-empty
element bsl corresponding to the ASCII character
‘<kbd>\</kbd>’ with a warning from the syntactic translator. Equivalents: <kbd>\brk;</kbd> for a
line break outside of a tabular environment.<a id="revfnote21" href="#fnote21">21</a>

</li>
<li> Blank line. Begin new paragraph command. Equivalent: <kbd>\parb</kbd> . Nearly equivalent: <kbd>\par</kbd> .

</li>
<li> “<kbd>``</kbd>” Left (double) quotation mark. Equivalent: <kbd>\ldq;</kbd> .

</li>
<li> “<kbd>''</kbd>” Right (double) quotation mark. Equivalent: <kbd>\rdq;</kbd> .

</li>
<li> “<kbd>$</kbd>” Begin math mode command. Equivalent: <kbd>\begin{math}</kbd> .

</li>
<li> “<kbd>$</kbd>” End math mode command. Equivalent: <kbd>\end{math}</kbd> .

</li>
<li> “<kbd>\[</kbd>” Begin displaymath mode command. Equivalent: <kbd>\begin{displaymath}</kbd> .

</li>
<li> “<kbd>\]</kbd>” End displaymath mode command. Equivalent: <kbd>\end{displaymath}</kbd> .

</li>
<li> “<kbd>.  </kbd>”, “<kbd>?  </kbd>”, “<kbd>!  </kbd>” End-of-sentence marks. Equivalent: <kbd>\eos;</kbd>, <kbd>\eoq;</kbd>, <kbd>\eoe;</kbd> . A period followed either by two blank spaces or by a newline
is recorded as an end of sentence. There is similar provision
for the question mark and the exclamation point. These tagged
forms may be used explicitly for the corresponding punctuation
inside math displays to distinguish punctuation from
mathematical use of the punctuation symbols. Explicit markup
for a comma is “<kbd>\cma;</kbd>”.<a id="revfnote22" href="#fnote22">22</a>


</li>
</ol>


</div>
</div>

<div class="subsection">
<h4>5.3.  <a id="SU-5.3"></a><a id="large"></a>Large Structure</h4>

Overall an article consists of a preamble followed by
a body. As <a href="#beginend">noted previously</a> (section 3.3) advanced mode
provides a special form of usage

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\begin{document} . . . \end{document}</kbd></td></tr></tbody></table></div>

with the paired metacommands begin and end that with an
article delimit its body. This is enabled with the
gellmu-trans call for the syntactic translator, and, consistent with regular
LaTeX usage the preamble is present without explicit tagging. 

The only required markup in a preamble is a title, and it
is formally correct for its content to be empty. The SGML content
model for a body is somewhat loose, but is usually understood
to consist of sections and may contain ordinary paragraphs
(par, which must be marked up explicitly, or parb,
which is begun with a blank line). Although a body may be entirely
empty (likely not useful) or may consist only of par and
parb elements, all inline text must be within one of these
basic paragraph containers. 

For example this formally correct textless document is handled without
noise by the didactic production system:

<dl class="verblist">
<dd><kbd>
\documenttype{article}</kbd></dd>
<dd><kbd>
\title{}</kbd></dd>
<dd><kbd>
\begin{document}\end{document}</kbd></dd>
</dl>

while the following document with text outside of a paragraph fails
initial validation in the didactic production system:

<dl class="verblist">
<dd><kbd>
\documenttype{article}</kbd></dd>
<dd><kbd>
\title{}</kbd></dd>
<dd><kbd>
\begin{document}</kbd></dd>
<dd><kbd>
x</kbd></dd>
<dd><kbd>
\end{document}</kbd></dd>
</dl>

The error may be corrected by placing a blank line before the
character ‘<kbd>x</kbd>’. 

The content model for preamble is tighter than that for
body. This makes it possible to have a greater level of
error-checking than would otherwise be possible. For example, a
preamble must have exactly one title although it is not
specified where in the preamble a title might be. There may be at
most one of each of the elements surtitle, subtitle, and
date. Although newcommand, which is a metacommand, does
not affect the document type definition and may be used at different
locations in the preamble, the small number of actual elements that
may be multiply used in the preamble, such as mathsym (which is
partly a metacommand) must be located together.

</div>

<div class="subsection">
<h4>5.4.  <a id="SU-5.4"></a><a id="sectioning"></a>Sectioning</h4>

In classical LaTeX one writes simply

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\section{Some title for a section}</kbd></td></tr></tbody></table></div>

to begin a new section. While this markup specifically delineates
the section title, LaTeX understands that a section has begun.
The section command has an option whose content is an alternate
title for the table of contents, and the starred form of the command
suppresses an otherwise automatic section number. 

With SGML the classical approach is something along the following
lines:

<dl class="verblist">
<dd><kbd>
<section><sectiontitle>Some title for a section</sectiontitle></kbd></dd>
<dd><kbd>
<para> A paragraph.</kbd></dd>
<dd><kbd>
<para> Another paragraph.</kbd></dd>
<dd><kbd>
     . . .</kbd></dd>
<dd><kbd>
</section></kbd></dd>
</dl>

Basic GELLMU markup corresponding to this would
be:<a id="revfnote23" href="#fnote23">23</a>

<dl class="verblist">
<dd><kbd>
\begin{section}\sectiontitle{Some title for a section}</kbd></dd>
<dd><kbd>
\para A paragraph.</kbd></dd>
<dd><kbd>
\para Another paragraph.</kbd></dd>
<dd><kbd>
    . . .</kbd></dd>
<dd><kbd>
\end{section}</kbd></dd>
</dl>

If, moreover, the markup is to be well-formed XML markup, then each
para tag would need explicit closure with <kbd></para></kbd>. 

The main point here is that the open and close tags for a section
in a classical SGML document type encompass the whole contents of
a section, and separate markup is required for the section
title.<a id="revfnote24" href="#fnote24">24</a>

The didactic SGML document type under advanced GELLMU seeks to
model classical LaTeX as closely as possible in order to provide a
bridge for authors from LaTeX to SGML (and, indeed, XML). For
this reason a command section similar to the classical LaTeX
command that delineates a section title is provided in the didactic
SGML document type. At the same time this document type has a whole
section container Section (upper case S) that in the
simplest case consists of a shead container for its title (or
header) followed by any number of paragraphs. The XML form of the
didactic document type supports only this latter tag, which means that
the translation script that converts SGML to XML has an unambiguous
way of performing the conversion from section to Section
provided that the author's source leads to an SGML instance which is
valid<a id="revfnote25" href="#fnote25">25</a>
under the didactic document type.

</div>

<div class="subsection">
<h4>5.5.  <a id="SU-5.5"></a><a id="labelref"></a>Labels, References, and Anchors</h4>

A label command may be placed anywhere that text may be placed
in order to mark a location and associate a symbolic “key”
with that location. A ref command may be placed anywhere that
text may be placed to generate a visible allusion called its
reference value, for example a section number, to the location
associated with a label key. An anch command may be placed
anywhere that text may be placed to provide a hypertext reference
either by key to an internal location or by uniform resource
identifier (URI) to an external resource. 

At this point the discussion will become descriptive of of the entire
didactic production system rather than simply of its document type.


<div class="subsubsection">
<h5>5.5.1.  <a id="SU-5.5.1"></a><a id="seq"></a>Labels and Sequencing</h5>

The basic usage for label is

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\label[:series="</kbd>
series-name
<kbd>" serseq="</kbd>
number
<kbd>" refkey="</kbd>
ref-key
"<kbd>]{</kbd>
key
<kbd>}</kbd></td></tr></tbody></table></div>

where use of the attributes is optional and, moreover, the required
key may be empty, i.e., the markup <kbd>\label{}</kbd> is permitted.
The key must be a case-sensitive string that is
monocase unique.<a id="revfnote26" href="#fnote26">26</a>
The didactic production system will provide a unique automatically generated string value
for key if none is provided by the author; this can be useful
if a series name is specified as an attribute for the label. 

An author should never reference a label key not provided by the
author, but the empty element popkey is intended for processing
evaluation as the last label key, automatic or not, preceding
its location. 

Sequencing<a id="revfnote27" href="#fnote27">27</a>
may be handled under the GELLMU didactic article
document type using labels and references. Toward this end one
makes use of three SGML attributes that are provided with the
label tag:

<dl>
<dt>
series</dt>
<dd>The value is the name of a sequenced family of labels.
A label may belong to at most one family, but there may be multiple
labels at the same location. There is no default value of series. </dd><dt>
serseq</dt>
<dd>The value is the sequence number of the label in its series
if a series is defined. It is meaningless if no series is specified
for the label. </dd><dt>
refkey</dt>
<dd>The name of a label key from which to spawn an automatically
generated value for the attribute serseq of the current label. </dd></dl>


Every label has a reference value that is normally accessed with
the ref command. This results in the creation, when
the XML version is generated, of an XML entity reference with name
based on the reference's key argument, that matches a CDATA
entity definition at the top of the XML document. The use of indirection
provided by this entity technique means that it is immaterial whether the
reference is forward or backward. 

The evalref command gives access to the literal value of a
reference without indirection, and places that value as a literal in
the XML version of an article. Thus, evalref is the name of a
tag only in the SGML document type and in the author-level XML document
type but not in the elaborated XML document type.
An evalref invocation will be successful only with a backward
reference. This is extremely useful for managing non-default
numbering of sectional units. For ordinary label references its use
is undesirable even though it is possible for backward references. 

The reference value of a label is determined as follows:

<ol class="decimal">
<li> Basic reference values are positive integers. Upper and lower
case alphabetic values and upper and lower case roman numeral values
may be obtained by applying the series command (not to be
confused with the series attribute for the label command)
to a basic reference value with type attribute of series
set to one of ‘<kbd>A</kbd>’, ‘<kbd>a</kbd>’, ‘<kbd>I</kbd>’, or ‘<kbd>i</kbd>’.

</li>
<li> If the label is assigned to a label series and is given a
refkey attribute, then the reference value of the label is the
reference value of the label referenced by the key that is the value
of the refkey. (This mechanism is used to re-start the
sequencing of the sectional unit id's at the end of this document.)

</li>
<li> Else if the label is assigned to a label series and the author
supplies an explicit literal numeric value for the
serseq attribute, then the value of serseq is its
reference value. (Markup — in particular, evalref —
cannot be used in defining an attribute value.)

</li>
<li> Else if the label is assigned to a label series, the reference
value of the label is the next (positive integer) value for a label
in that series. (This mechanism is used to control the sectional
id of the last section of this document. It may also be used to
run parallel interleaved sequences of sectional units, such as, for
example, questions and answers, within a document.)

</li>
<li> Else the reference value of the label is the sectional unit
identifier, i.e., its sunit value rather than the logical
value in its attribute sid, of the smallest sectional
unit containing the label. These values may not be numeric. For
example the string “A.3.2” might be a sectional unit
identifier. The series command should not be used to express
type conversion of a reference value that might resolve as a sectional
unit identifier.

</li>
</ol>


</div>

<div class="subsubsection">
<h5>5.5.2.  <a id="SU-5.5.2"></a>Anchors</h5>

The basic usage for anch is

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\anch[</kbd>
reference specs
<kbd>]{</kbd>
anchored text
<kbd>}</kbd></td></tr></tbody></table></div>

where the option, which is not an attribute option but rather
becomes the element anchref in XML (while the anchor's argument
— its “presented content” — becomes anchv), is
expected to contain white space separated strings of the form
<kbd>name="value"</kbd><a id="revfnote28" href="#fnote28">28</a>
with name restricted to one of the following:

<dl>
<dt>fref</dt>
<dd> A footnote reference. Value is a string
that becomes the content of an automatically created
footnote to the text in anchv. This usage is deprecated;
use \footnote instead.
</dd>
<dt>href</dt>
<dd> A web reference as with href in HTML.
That is, value is a URI. It could be of the form
“<kbd>#labelkey</kbd>” where “<kbd>labelkey</kbd>” is the name of a label
key that is preferably and more easily used with iref.
(The ‘<kbd>#</kbd>’ needs to be escaped, i.e., marked up as
“<kbd>\#</kbd>”.) In a non hypertext formatting the URI
may be presented as a note or footnote associated with the text in
anchv.
</dd>
<dt>Href</dt>
<dd> Same as href except that the author wishes
to suppress any note or footnote presentation of the URI. This
might be the case if, for example, the URI might be obviously
deducible from the anchv content.
</dd>
<dt>iref</dt>
<dd> An internal reference; value must be a label key arising
from label or klabel<a id="revfnote29" href="#fnote29">29</a>. </dd>
</dl>

Note also that there is a command urlanch (probably should have
been urianch), taking a single argument, used for URIs,
which is intended to have the same effect as a newcommand with
one argument for creating a web anchor with the URI as presented
content.

</div>

<div class="subsubsection">
<h5>5.5.3.  <a id="SU-5.5.3"></a><a id="counters"></a>Example Emulating a LaTeX Counter</h5>

Suppose that one wants to fashion an inline enumerated list at some
point in a document. An enumerate environment is a list
structure that, while it may occur in a paragraph, is not inline. The
idea is to give each item a label and fashion the inline list item
number by referencing that label. One writes a newcommand to ease
this. 

The name of a LaTeX counter is emulated with the name of the
series attribute for one or more labels. Unless one wishes to
be able to reference the items apart from the immediate reference, one
need not provide a label key. The didactic production system will provide a default labelkey
and the command “<kbd>\popkey</kbd>”, which grabs the key of the last preceding
label, may be used to furnish the key for the immediate reference.
If one wants small Roman numerals, one wraps the “<kbd>\ref</kbd>” command
in a “<kbd>\series</kbd>” command. Since series requires an actual
number, one must use evalref instead of ref, which is
permitted so long as the reference follows the label.
Here's the markup:

<dl class="verblist">
<dd><kbd>
\label[:series="foo" serseq="0"]{} % zero the counter named foo</kbd></dd>
<dd><kbd>
\newcommand{\ti}{%</kbd></dd>
<dd><kbd>
\label[:series="foo"]{}(\series[:type="i"]{\evalref{\popkey}})}</kbd></dd>
<dd><kbd>
Hilbert's three most important contributions to algebraic geometry</kbd></dd>
<dd><kbd>
are \ti~the basis theorem, \ti~the nullstellensatz, and \ti~the syzygy</kbd></dd>
<dd><kbd>
theorem.</kbd></dd>
</dl>

The rendering is this:
<a id="KEY-1"></a>

Hilbert's three most important contributions to algebraic geometry
are <a id="KEY-2"></a>(i) the basis theorem, <a id="KEY-3"></a>(ii) the nullstellensatz, and <a id="KEY-4"></a>(iii) the syzygy
theorem. 

With the current didactic production system if one had used “<kbd>\ref</kbd>” instead of
“<kbd>evalref</kbd>”, the translator from author-level XML to elaborated
XML, which resolves references, would have issued a warning in the
scroll, but the build would have run to otherwise successful completion
by ignoring the presence of the series command.

</div>
</div>

<div class="subsection">
<h4>5.6.  <a id="SU-5.6"></a><a id="secusage"></a><a id="last"></a>General Usage for Sectional Units</h4>

This describes the content model in the GELLMU didactic document type
for the “whole” sectional units Section,
Subsection, … as fully tagged.


<div class="subsubsection">
<h5>5.6.1.  <a id="SU-5.6.1"></a><a id="seccontent"></a>The Content Model</h5>

The content model for sectional units is:

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>((sopt)?,(sprefix)?,(sunit)?,(shead),(%UnitContent)*)</kbd></td></tr></tbody></table></div>

where:

<dl>
<dt>%UnitContent</dt>
<dd> refers to the subsections, loose paragraphs, and other general content
that is allowed inside a section.
</dd>
<dt>shead</dt>
<dd> is the required<a id="revfnote30" href="#fnote30">30</a>
section header or title.
</dd>
<dt>sopt</dt>
<dd> is an optional title for use in the table of
contents<a id="revfnote31" href="#fnote31">31</a>.
</dd>
<dt>sprefix</dt>
<dd> is optional markup for text that is to precede the sectional unit
sequence notation. For example, if the sectional unit sequence is
“B” and sprefix is the markup string
“<kbd>Appendix </kbd>” (ending with a blank space), then the visible
indicator for the sectional unit, when consistent with the setting of
secnumdepth, is “Appendix B” both at the beginning
of the section and in the table of contents. Or if the sequence is
“3” and the sprefix is “A”, then the
visible indicator is “A3”.
</dd>
<dt>sunit</dt>
<dd> is an optional setting for the sectional unit sequence. The GELLMU
didactic document type has an attribute “sid” for the
sectional units Section, Subsection, … that is
optional (and rare for author usage) in the SGML version but
required in the XML version. The translator from SGML to XML
computes it in the standard way. For example subsubsection 1 of
subsection 3 in section 2 acquires the sid “2.3.1”.
It is expected that formatters will use this value for the visible
sectional unit indicator, preceded, as previously described, by
any sprefix, unless the user provides sunit. While
sunit is intended to override the visible indicator, it is
not provided to override the sid attribute itself which a
formatter should see as describing logical structure. </dd>
</dl>


</div>

<div class="subsubsection">
<h5>5.6.2.  <a id="SU-5.6.2"></a><a id="ltxsecusage"></a>The LaTeX-Like Form of General Usage</h5>

Corresponding LaTeX-like argument/option syntax can be used, as previously
indicated, in GELLMU source with section, subsection,
… . If, however, argument/option syntax is used, one must be mindful of
the ordering of the options, and use empty option brackets, as
necessary, to indicate the position in the sequence of an option with
content. For example, a sole option is understood as sopt, the
version of the sectional unit title to be used in the table of
contents. To provide only sprefix with argument/option syntax one
precedes the bracket sequence for sprefix with an empty pair
“<kbd>[]</kbd>” of option brackets<a id="revfnote32" href="#fnote32">32</a>
for sopt.

</div>
</div>

<div class="subsection">
<h4>5.7.  <a id="SU-5.7"></a><a id="verb"></a>verbatim, verblist, and
manmac</h4>

The ordinary notion of “verbatim” is complicated in the
context of a document type that is intended for processing toward
multiple output formats. There is no special provision for verbatim
markup under basic GELLMU<a id="revfnote33" href="#fnote33">33</a>,
but there are two layers, one simplistic and one sophisticated, in the
didactic production system with each layer having provision for both inline and block-level
verbatim markup. 

The simplistic approach involves the provision of an inline element
verb and a block-level element verbatim in the didactic document type.
With these the author is responsible for entering special characters
in ways that are safe for input source notation, safe for syntactic translator
output, and safe for each output format that is envisioned.<a id="revfnote34" href="#fnote34">34</a>
In the simplistic layer the formatting program in the didactic production system for HTML
output renders verb as an HTML kbd element and
verbatim as an HTML pre element. In formatting for
regular LaTeX output each of these SGML elements is rendered
as its LaTeX namesake. Neither the pre element in HTML
nor the (basic) verbatim command in LaTeX is context-sensitive,
and typically are formatted with left margin justification. 

The sophisticated layer in the syntactic translator for verbatim is enabled by
setting the variable gellmu-verbatim-clean true. If this is
the case, then a user should input verbatim material literally between
<kbd>\begin{verbatim}</kbd> and <kbd>\end{verbatim}</kbd> markers occupying whole lines
and the syntactic translator will convert each of the 33 non-alphanumeric printable
ASCII characters therein to the corresponding empty element in
the didactic document type, and render each line of the converted material as a list
item bearing the item name nln in a list element
verblist.<a id="revfnote35" href="#fnote35">35</a>

Similar arrangements pertain to the sophisticated inline analogue
of verb, which is enabled in the syntactic translator by setting the variable
gellmu-manmac-bar-name to a non-empty string value that is
to become the name of the element, such as quostr, to contain
the content, which should be delimited in source by successive
‘<kbd>|</kbd>’ characters. By default the user must enter a
verbatim string in “safe” form, but may enter it,
apart from any occurrence of the character ‘<kbd>|</kbd>’, literally
if the variable gellmu-manmac-literal is true. The term
“manmac” is derived from an old plain TeX package for
writing documentation by that name in which the character ‘<kbd>|</kbd>’
is used to delimit inline literal material for verbatim presentation.
Moreover, consistent with usage observed in LaTeX documentation
markup of the form

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\</kbd>name<kbd>|</kbd>literal-text<kbd>|</kbd></td></tr></tbody></table></div>

is translated by the syntactic translator to an element named as with simple
“<kbd>|...|</kbd>” having a setting for its attribute
with name the value of the string variable
gellmu-manmac-attribute, which for quostr in the didactic document type
would appropriately be its attribute inv. 

Variable settings to provide for the use of literal input both for
verbatim as a metacommand front for the list element
verblist and manmac configuration for the element
quostr, as described, are default when the syntactic translator is begun with
the non-default function gellmu-latex-faq. This function also
sets the variable gellmu-squophrase-name, which otherwise
defaults to the empty string, to the value “<kbd>squophrase</kbd>”.
This causes the syntactic translator to attempt to interpret balancing
character pairs consisting of the character ‘<kbd>‘</kbd>’ and the
character ‘<kbd>’</kbd>’ as delimiters for the element
squophrase, an alternate form along with quophrase,
for “quoted phrase”, with odd instances of the character
‘<kbd>’</kbd>’ set as the empty element apos, which represents
an apostrophe.

</div>

<div class="subsection">
<h4>5.8.  <a id="SU-5.8"></a><a id="accents"></a>Accents</h4>

Traditional LaTeX markup employs accent commands for modifying
ASCII characters in order to produce non-ASCII
characters. On the other hand characters from 16
“byte-planes” of Unicode are now available in HTML
and XML as ordinary characters, with treatment as the atoms of
ordinary strings of text not requiring any special attention or notice
from the viewpoint of markup. It may happen that this will affect
development in the LaTeX project, and it is, therefore, unclear what
the long term role might be of LaTeX's accent commands. 

Nonetheless, the didactic document type provides element names corresponding to the
14 classical LaTeX accents although it does not provide classical
markup notations such as “<kbd>\'</kbd>”,
“<kbd>\"</kbd>”, “<kbd>\~</kbd>”, … inasmuch
as names are required in syntactic translator output.<a id="revfnote36" href="#fnote36">36</a>
The names for the accents may be seen by locating the word
“accent” in the didactic production system file <kbd>gellmu.dtd</kbd> and reading
the following 14 lines. 

An author, particularly an author residing in an English language
locale, may introduce, for example, the character é in
several ways:

<ol class="decimal">
<li> by using an algorithmic accent command — in this case
<kbd>\acute{e}</kbd>: é. 
</li>
<li> by direct Unicode-based entity reference – in this case
<kbd>&#xE9;</kbd>: é. 
</li>
<li> by simple direct entry of the Unicode point in a file
having the UTF-8 text encoding. 
</li>
</ol>

Note that Unicode values are numbers represented in hexadecimal
notation (base 16); the digits are 0–9 and A–F. Thus, E9 is
233, and one could also use the entity reference <kbd>&#233;</kbd>. 

While for the long term, the largely equivalent<a id="revfnote37" href="#fnote37">37</a>
second or third methods are superior,
there are caveats for their use in 2007:

<ul>
<li> One's LaTeX back end must have a suitably robust way
of handling Unicode, presumably via the inputenc
package or possibly via Omega/Lambda.

</li>
<li> Even when fonts are available, some web browsers
seem only to handle Unicode via entity references. 
</li>
</ul>



</div>

<div class="subsection">
<h4>5.9.  <a id="SU-5.9"></a><a id="tabular"></a>Tabular Environment Emulation</h4>

At this point (2006-7) the didactic document type is able to accomodate emulation
of LaTeX's tabular environment with “<kbd>l</kbd>”, “<kbd>c</kbd>”,
“<kbd>r</kbd>”, and “<kbd>p</kbd>” column cell specifiers with, where
robust CSS support is available for HTML, “<kbd>|</kbd>” indicators
for vertical cell rules and “<kbd>\hline</kbd>” commands for horizontal
rules between rows. While multicol, and multirow are not
modeled, cells may contain other tabulars recursively. 

A “<kbd>p</kbd>” column specifier optionally takes a decimal argument
that represents the fraction of available width to be made available
for the cells in that column. When is no fractional width specifier,
the default fractional width is <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mfrac
><mn>1</mn><mrow><mi>n</mi><mo>+</mo><mn>1</mn></mrow
></mfrac
></math
> where <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mi>n</mi></math
> is the
total of number of columns. 

What may be viewed as a shortcoming of the tabular emulation
is that in each tabular row the first cell must contain
some markup in order for the document to be structurally correct.
This arises from a rule associated with SGML document types
that might be overcome if GELLMU source were processed by a
monolithic program. Instead, however, it is an
assemby of <a href="#flow">separate components</a> (appendix 7.5.2) in which the first stage
has knowledge of syntax but not of the markup vocabulary. 

One thing to keep in mind with tabular is that in the current,
though probably not future, design of HTML tables are not allowed
in paragraph content. The didactic production system works hard to deal with this. In most
web browsers there will be a line break before an HTML table and
again after an HTML table. (One way to finesse that is to place a
table in a cell in a sur-table, which is abuse of markup.) This
author generally places a tabular inside a display,
which is the GELLMU object corresponding to LaTeX's center. 

The document type does not offer “floating” objects, and, therefore,
the name table is not used as as in LaTeX. 

The name table is used for emulation in regular GELLMU
source of HTML tables. A table, like a tabular,
takes a required argument consisting of column specifiers.
In the didactic production system at the point where an article is spun to the elaborated
XML version of article, there is no longer a distinction
between tabular and table. 

There is also array, which, as in LaTeX, is the in-math
version of tabular, except that in GELLMU its emulation of
LaTeX's array survives translation to the XML version of
article. An array has only “<kbd>l</kbd>”, “<kbd>r</kbd>”,
and “<kbd>c</kbd>” cells. 

Example: The markup for the <a href="#dtdfiles">table of DTD's</a>
in Appendix B.2.2 is this:

<dl class="verblist">
<dd><kbd>
\begin{display}</kbd></dd>
<dd><kbd>
\begin{tabular}{l|cc}</kbd></dd>
<dd><kbd>
~                       & Latin-1              & \abbr{UTF-8}          \\</kbd></dd>
<dd><kbd>
\hline</kbd></dd>
<dd><kbd>
First stage \abbr{SGML} &  \quostr{gellmu.dtd} &  \quostr{ugellmu.dtd} \\</kbd></dd>
<dd><kbd>
Author Level \abbr{XML} &  ~                   & \quostr{axgellmu.dtd} \\</kbd></dd>
<dd><kbd>
Elaborated \abbr{XML}   & \quostr{xgellmu.dtd} & \quostr{uxgellmu.dtd}</kbd></dd>
<dd><kbd>
\end{tabular}</kbd></dd>
<dd><kbd>
\end{display}</kbd></dd>
</dl>

Because the one horizontal divider and the one vertical divider rely
on CSS support in HTML, these dividers might not be seen in a web
browser with weak CSS support.

</div>

<div class="subsection">
<h4>5.10.  <a id="SU-5.10"></a><a id="graphics"></a>Graphic Inclusions</h4>

There is basic support for graphics inclusions suitable for the HTML
backend and the LaTeX backend with both DVI and PDF outputs.
The arrangements are not unlike those required for the use of
the includegraphics command provided by LaTeX's
graphicx package. This means that, apart from the didactic production system's chain
of processors, one needs to provide several different versions of a
given graphic object in order to accommodate the needs of the three
different output formats (HTML, PDF, and DVI). A reliable graphics
format converter such as that provided by ImageMagick
(<a href="http://www.imagemagick.org/"><kbd>http://www.imagemagick.org/</kbd></a>)
or the netpbm utilities
(<a href="http://netpbm.sourceforge.net/"><kbd>http://netpbm.sourceforge.net/</kbd></a>)
and a broad TeX support environment similar to that provided by
TUG's <a href="http://www.tug.org/texlive/">TeXLive</a>
are essential for work with included graphics. 

For example, if one begins with an encapsulated PostScript image
<kbd>glmy.eps</kbd> made, say, with Metapost, then one might run
the commands

<dl class="verblist">
<dd><kbd>
   epstopdf glmy.eps</kbd></dd>
<dd><kbd>
   convert glmy.pdf glmy.png</kbd></dd>
</dl>

before making PDF with pdflatex and PNG (for inclusion
in HTML). In this case the PDF version of the graphic should be
regarded as best for use with pdflatex, and so one wants to
have the PNG version out of view from pdflatex when
building the GELLMU source <kbd>glman.glm</kbd> for this document.
With the new mmkg drivers one may prepare a tiny file
<kbd>glman.prx</kbd> that is a list of names of image files, one file
per line, that should be out of view at the point in the pipeline when
pdflatex is active. Thus, a line in the file
<kbd>glman.prx</kbd> should contain the name <kbd>glmy.png</kbd>. 

In <a href="glman.glm"><kbd>glman.glm</kbd></a> one has the
code:

<dl class="verblist">
<dd><kbd>
\begin{quotation}</kbd></dd>
<dd><kbd>
   Sometimes a picture is worth a thousand words.</kbd></dd>
<dd><kbd>
   \display[:frame="1.1"]{\includegraphics[:scale="0.2"]{glmy}}</kbd></dd>
<dd><kbd>
\end{quotation}</kbd></dd>
</dl>

which yields:
<blockquote>

Sometimes a picture is worth a thousand words.

<div class="display"><table class="gdisplay" style="padding: 1ex; border: 0.3ex solid;"><tbody><tr><td>
<img src="glmy.png" alt="Image file: glmy.png" />
</td></tr></tbody></table></div>

</blockquote>


In this markup one sees, first of all, two uses of SGML
attributes — frame and scale. Attribute
options are opened with “<kbd>[:</kbd>” rather than simply with
“<kbd>[</kbd>”. Whereas options generally may contain markup,
attribute options may not. 

The meaning in this example of scale is that the width
of the graphic in DVI and PDF outputs will be the result
of multiplying the scale by LaTeX's value of
\textwidth.<a id="revfnote38" href="#fnote38">38</a>
The HTML formatter will link to the PNG without a width
specification. Thus, the brower window width of the graphic will be
the actual width of the PNG image unless, perhaps, it's too large for
the browser's window. The meaning of frame is that for print
outputs the graphic image will be surrounded by a LaTeX
framebox with diameter that is <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>1.1</mn></math
> times the diameter of the
display's content. In the current HTML formatter no use is
made of the numeric value of frame although a default frame is
constructed via an HTML attribute giving values for the CSS
properties border and padding. When image framing is
desired, another approach is to incorporate framing in the graphic
itself.

</div>
</div>

<div class="section">
<h3>6.  <a id="SU-6"></a><a id="math"></a>Mathematics in article</h3>

<div class="subsection">
<h4>6.1.  <a id="SU-6.1"></a><a id="genmath"></a>General</h4>

There was previous mention of the basic mathematical container element
tmath in the discussion of <a href="#single">single string</a> (section 5.2.2) markup
and the math and displaymath elements in the discussion
of <a href="#certainstrings">certain strings</a> (section 5.2.3) of special markup
significance. 

The markup used inside these containers is very similar to that
which is used in LaTeX although far from all of LaTeX's math
markup, as extended by the amsmath package, has any
analogue in the didactic production system. 

There are a few things that deserve short mention:

<dl>
<dt>\sum, \int, and \prod</dt>
<dd> are all similar to
their LaTeX namesakes except that each requires explicit closure.
For example,

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\[ \sum_{0}^{\infty} \frac{x^k}{k!} \sum: \]</kbd></td></tr></tbody></table></div>

produces

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block" mode="display"
><mrow><munderover><mo>∑</mo><mn>0</mn><mi>∞</mi></munderover><mfrac
><mrow><msup><mi>x</mi><mi>k</mi></msup
></mrow
><mrow><mi>k</mi><mo>!</mo></mrow
></mfrac
></mrow
><mspace width="0.6em"/><mtext>.</mtext
></math>

</dd>
<dt>\regch, \mbox, and \text</dt>
<dd> The didactic document type provides regch,
for “regular character” that is a one character version
of mbox provided for separating from general
mbox matter the content to which a non-math
<a href="#accents">algorithmic accent</a> (section 5.8), may
be applied. For example,
<dl class="verblist">
<dd><kbd>
\newcommand{\Q}{\regch{\bold{Q}}}  % intended for use in math</kbd></dd>
<dd><kbd>
\newcommand{\galQ}{\mbox{Gal}(\ovbar{\Q}/\Q)}  % only in math</kbd></dd>
<dd><kbd>
$\galQ$\aos;</kbd></dd>
</dl>

produces

<math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mi>Gal</mi><mfenced open="(" close =")"
><mrow><mover accent="true"><mi mathvariant="bold" fontweight="bold" fontstyle="normal">Q</mi><mo>¯</mo></mover
><mo stretchy="true" lspace="0.3em" rspace="0.3em">⁄</mo><mi mathvariant="bold" fontweight="bold" fontstyle="normal">Q</mi></mrow></mfenced
></math
>.

Both regch and mbox should be used only for symbols.
Note that “Gal” in the foregoing is a symbol. The command
\text is provided for the use of text phrases – usually conjunctive
in nature – inside math zones. For example, the markup

<dl class="verblist">
<dd><kbd>
\[ \absval{x} = \lbalbr{\begin{array}{rl}</kbd></dd>
<dd><kbd>
             x & \text{\ if\ } x \geq 0 \\</kbd></dd>
<dd><kbd>
            -x & \text{\ if\ } x < 0</kbd></dd>
<dd><kbd>
            \end{array}} \]</kbd></dd>
</dl>

produces

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block" mode="display"
><mfenced open="|" close="|"><mi>x</mi></mfenced><mo>=</mo><mfenced open="{" close =""
><mtable
><mtr><mtd columnalign="right"><mi>x</mi></mtd
><mtd columnalign="left"><mtext
> if </mtext
><mi>x</mi><mo>≥</mo><mn>0</mn></mtd
></mtr><mtr><mtd columnalign="right"><mo>−</mo><mi>x</mi></mtd
><mtd columnalign="left"><mtext
> if </mtext
><mi>x</mi><mo><</mo><mn>0</mn></mtd
></mtr></mtable
></mfenced
></math>

In this example note that the command name lbalbr stands for
“left balanced brace”. It corresponds to
the use of <kbd>\left\{  ...  \right.</kbd> in LaTeX<a id="revfnote39" href="#fnote39">39</a>.

</dd>
<dt>\aos;, \aoc; \aoq;, and \aoe;</dt>
<dd> are the
named forms of the LaTeX space adjustment commands “<kbd>\@.</kbd>”,
“<kbd>\@,</kbd>”, “<kbd>\@?</kbd>”, and “<kbd>\@!</kbd>”, which
provide correct placement of inline punctuation immediately following
inline mathematical markup. There is now also default provision in the
didactic production system for the more LaTeX-like “<kbd>\@</kbd>” usage. Note that the
use of <kbd>\@</kbd> is seldom necessary.
</dd>
</dl>


</div>

<div class="subsection">
<h4>6.2.  <a id="SU-6.2"></a><a id="assert"></a>Assertions: Near Emulation of
LaTeX's Theorem-Like Environments</h4>

<div class="subsubsection">
<h5>6.2.1.  <a id="SU-6.2.1"></a>Examples</h5>

The container element \assertion is used in the didactic document type for the
creation of its analogue under SGML of theorem-like environments. As
a first example of the near emulation of a LaTeX theorem-like
environment, here is markup to give LaTeX-like meaning to
“<kbd>\begin{theorem}</kbd>” and “<kbd>\end{theorem}</kbd>”.

<dl class="verblist">
<dd><kbd>
\newcommand{\begin{thm}}[1][]{%</kbd></dd>
<dd><kbd>
\begin{assertion}[#1][theorem]{Theorem}[\evalref{\popkey}]}</kbd></dd>
<dd><kbd>
\newcommand{\end{thm}}{\end{assertion}}</kbd></dd>
</dl>


For a first instance it is invoked without supplying the optional first
argument, which is for a label key.
<a id="AssertLabel-1"></a>
<dl class="assertion">
<dd>
Theorem 1.
  The continued fraction expansion of a real number is finite
if and only if the real number is a rational number. </dd></dl>

This is just text to follow the statement of a theorem. 

If we do the same thing again, the theorem number should go up by
<math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>1</mn></math
> since in the didactic production system this usage is equivalent to using the default
counter associated with a label series name theorem.<a id="revfnote40" href="#fnote40">40</a>
<a id="AssertLabel-2"></a>
<dl class="assertion">
<dd>
Theorem 2.
  The continued fraction expansion of a rational number is
eventually periodic if and only if the real number is an irrational
number that is the root of some quadratic polynomial with rational
coefficients. </dd></dl>


</div>

<div class="subsubsection">
<h5>6.2.2.  <a id="SU-6.2.2"></a><a id="assertion"></a>Usage for assertion</h5>

The general usage of assertion is the following:

<dl>
<dd> <kbd>\begin{assertion}[</kbd>key<kbd>][</kbd>series
<kbd>]{</kbd>name<kbd>}[</kbd>id<kbd>]</kbd></dd>
<dd> <kbd>  .  .  .</kbd></dd>
<dd> <kbd>\end{assertion}</kbd></dd>
</dl>

The options key and series represent the same things as
the corresponding <a href="#seq">label</a> (section 5.5.1) options. The id
option is for explicit customization of the visible identifier, e.g.,
theorem number, as illustrated with one of the examples later in this
section. One may use the id option, which must follow
the name argument, without using either of the other options. But in
order to use the series option, a key option, which may
simply be empty, must be present. 

There is also a fully named way to proceed:

<dl>
<dd> <kbd>\begin{assertion}</kbd></dd>
<dd> <kbd>\asstkey{. . .}\asstser{. . .}\asstname{. . .}\asstid{. . .}</kbd></dd>
<dd> <kbd>  .  .  .</kbd></dd>
<dd> <kbd>\end{assertion}</kbd></dd>
</dl>

Here order is important, but any of the options may simply be omitted.
For example, we may write

<dl class="verblist">
<dd><kbd>
\newcommand{\begin{Thm}}[1]{%</kbd></dd>
<dd><kbd>
\begin{assertion}\asstser{#1}\asstname{Theorem}%</kbd></dd>
<dd><kbd>
\asstid{\sref;.\evalref{\popkey}}%</kbd></dd>
<dd><kbd>
}</kbd></dd>
<dd><kbd>
\newcommand{\end{Thm}}{\end{assertion}}</kbd></dd>
<dd><kbd>
\begin{Thm}{XXseries}</kbd></dd>
<dd><kbd>
If $[ n_1, n_2, \ldots ]$ is an infinite continued fraction, then</kbd></dd>
<dd><kbd>
its sequence of convergents always has a limit.</kbd></dd>
<dd><kbd>
\end{Thm}</kbd></dd>
</dl>

to obtain:

<a id="AssertLabel-3"></a>
<dl class="assertion">
<dd>
Theorem 6.2.2.1.
  If <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mfenced open="[" close ="]"
><mrow><msub><mi>n</mi><mn>1</mn></msub
><mo>,</mo><msub><mi>n</mi><mn>2</mn></msub
><mo>,</mo><mi>…</mi></mrow></mfenced
></math
> is an infinite continued fraction, then
its sequence of convergents always has a limit. </dd></dl>

Notice that the asstid argument is merging the reference value
for (the new) series XXseries with the visible id of the
current sectional unit.

</div>
</div>

<div class="subsection">
<h4>6.3.  <a id="SU-6.3"></a><a id="eqn"></a>Equations and Equation Arrays</h4>

The general usage for equation is the following:

<dl>
<dd> <kbd>\begin{equation}[</kbd>key<kbd>][</kbd>series<kbd>]</kbd></dd>
<dd> <kbd>  .  .  . </kbd></dd>
<dd> <kbd>\end{equation}</kbd></dd>
</dl>

The options key and series represent the same things as
the corresponding <a href="#seq">label</a> (section 5.5.1) options. In order to use
the series option, a key option, which may simply be
empty, must be present. The use of “<kbd>equation*</kbd>” as a name for an
equation display that is not numbered is
not permitted, but one may instead use the nonum attribute
as follows:

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\begin{equation}[:nonum="true"] . . . \end{equation}</kbd> .</td></tr></tbody></table></div>


General usage for an equation array (name eqnarray) is:

<dl>
<dd> <kbd>\begin{eqnarray}[</kbd>key<kbd>][</kbd>series<kbd>]</kbd></dd>
<dd> <kbd>  .  .  . </kbd></dd>
<dd> <kbd>\end{eqnarray}</kbd></dd>
</dl>

where the content is an eqnabody consisting of eqnrow's,
each row may be terminated in LaTeX-like markup, as in LaTeX, with the
string “<kbd>\\</kbd>” and consists of three parts, corresponding to elements
eqnleft, eqncenter, and eqnright, that may
be separated in LaTeX-like markup with the character ‘<kbd>&</kbd>’. 

Support for numbering in eqnarrays is only minimally developed
although there is suggestive sketching in the didactic document type that is not
supported in the formatters. By default the equations in equation
arrays are numbered consecutively throughout an article. This
behavior can be altered by using the series attribute of an
eqnarray. If that is done, then, as things have been sketched,
numbering applies to whole arrays rather than to the equations within
arrays. Numbering in an equation array may be suppressed by setting
its attribute nonum to the string “<kbd>true</kbd>”.

</div>

<div class="subsection">
<h4>6.4.  <a id="SU-6.4"></a><a id="mathsym"></a>The \mathsym Metacommand</h4>

mathsym is a macro substitution metacommand that is
available in the didactic production system for enabling an author to declare that a macro
name represents a mathematical symbol. It is a formal way of
recording statements commonly made by authors in introducing notation. 

Unlike regular metacommands, which may appear at any point in
GELLMU source, mathsym may only appear in the preamble
of an article, or, equivalently with defaults in the
syntactic translator, mathsym may only appear before the LaTeX-like
“<kbd>\begin{document}</kbd>”. 

Its usage is:

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>\mathsym{</kbd>
symbol-name
<kbd>}{</kbd>
symbol-rendering
<kbd>}[</kbd>symbol-meta-info
<kbd>]</kbd> . </td></tr></tbody></table></div>


Here symbol-name is an alphanumeric string (case-sensitive)
beginning with a letter. The second argument is the presentation
rendering of the symbol in GELLMU markup. It is like the definition
of a newcommand except that it may not involve
arguments.<a id="revfnote41" href="#fnote41">41</a>
The optional third argument symbol-meta-info is an
alpha-numeric string that might also include possibly a few other
string characters such as ‘<kbd>/</kbd>’, ‘<kbd>-</kbd>’, ‘<kbd>,</kbd>’,
‘<kbd>.</kbd>’, ‘<kbd>*</kbd>’, etc. Its exact structure depends on the
typing system. (No typing system is part of the didactic production system.) For example,
it might consist of (name, value) pairs for conveying meta-information
about the symbol. 

The syntactic translator replaces each invocation of a given
mathsym with the specified rendering and writes for each
mathsym definition a corresponding element in the SGML output
whose content consists solely of the declared symbol name if there is
no meta information but otherwise consists of the symbol name followed
by a blank space and then whatever string of meta information is
provided in the optional argument. Additionally, each invocation is
wrapped in a rendering-inert Sym element whose key
attribute reveals the name given to the symbol at the point of
declaration (and by which the symbol is invoked). This makes it
possible for a downstream authoring platform processor that has
remembered the list of declared symbol names to match each invocation
of a declared symbol with its associated meta information, if any,
provided by the author in the symbol declaration. 

A related feature in the didactic GELLMU document type is the
mlg tag for marking mathematical logical groups. This is
somewhat akin to the lgg tag for TeX-like logical groups,
traditionally created in TeX markup with braces that are not
attached to a command.<a id="revfnote42" href="#fnote42">42</a>
As with lgg there is no obvious evidence of an mlg tag
in a typeset rendering, but the presence of such a tag is intended as
a signal to downstream mathematical parsers that the contents of the
tag be given grouping priority as, say, with visible parentheses.
Furthermore, the mtype and mml attributes of the
mlg tag may be used to pass semantic information about the
tag's contents to a processor.

</div>
</div>

<div class="section">
<h3>7.  <a id="SU-7"></a><a id="dps"></a>The Didactic Production System</h3>

The didactic production system is the suite of processors and technical support files
underlying what is called regular GELLMU.


<div class="subsection">
<h4>7.1.  <a id="SU-7.1"></a>Permission</h4>

The items of the didactic production system are copyrighted free software released
under the <a href="http://www.gnu.org/copyleft/">GNU General Public License</a>.

</div>

<div class="subsection">
<h4>7.2.  <a id="SU-7.2"></a><a id="materials"></a>Materials</h4>

The release contains everything originating with the author that is
currently used in “building” GELLMU documents. 

It also contains a slightly <a href="../perllib/SGMLS.pm">modified version</a>
of David Megginson's Perl module “<kbd>SGMLS.pm</kbd>” based on
another slightly modified version that was furnished to me by Dave
Holden in a very quick early 1999 response to my posted request for a
modification that handles the labels provided (optionally) by
nsgmls for SGML elements that are defined empty. A similar
slight modification was also supplied a few days later by Vassilii
Kachaturov and had been available at his web site. 

Although the materials offered in this package aside from the syntactic translator
pertain only to the didactic document type and the didactic production system, it should be understood that
the larger design for GELLMU envisions other parties, on the one
hand, building in various ways to extend the functionality of the
didactic system, and, on the other hand, applying the methods of the
didactic system to other document types and other formatting programs
for those document types. 

The basic items originating with the author, aside from the document
type definition <a href="#dtdfiles">files</a> (section B.2.2) are:

<dl>
<dt><a href="../gellmu.el"><kbd>gellmu.el</kbd></a></dt>
<dd>the GELLMU syntactic translator, which makes SGML</dd>
<dt><a href="../xplaingart.pl"><kbd>xplaingart.pl</kbd></a></dt>
<dd>converts SGML to
author-level XML</dd>
<dt><a href="../xmlgart.pl"><kbd>xmlgart.pl</kbd></a></dt>
<dd>converts author-level XML
to elaborated XML</dd>
<dt><a href="../ltxgart.pl"><kbd>ltxgart.pl</kbd></a></dt>
<dd>translates elaborated XML
to LaTeX</dd>
<dt><a href="../htmlgart.pl"><kbd>htmlgart.pl</kbd></a></dt>
<dd>translates elaborated XML
to classical HTML and translates specially prepared XML to XHTML+MathML</dd>
<dt><a href="../mathcdata.pl"><kbd>mathcdata.pl</kbd></a></dt>
<dd>first of two special
preparations for translation toward XHTML+MathML</dd>
<dt><a href="../mathprep.pl"><kbd>mathprep.pl</kbd></a></dt>
<dd>second of two special
preparations for translation toward XHTML+MathML</dd>
<dt><a href="../mval.pl"><kbd>mval.pl</kbd></a></dt>
<dd>check for certain types of MathML errors</dd>
</dl>


Since some users will only be interested in the syntactic translator, additional
description of these materials is found below in
<a href="#usingdps">“Using the didactic production system”</a> (section 7.5) and in the
<a href="#release">Release Notes</a> (appendix B).

</div>

<div class="subsection">
<h4>7.3.  <a id="SU-7.3"></a><a id="requiredsoftware"></a>Other Required Software</h4>

To make use of the GELLMU syntactic translator a user must have or separately acquire
<a href="http://www.gnu.org/software/emacs/">Emacs</a>.<a id="revfnote43" href="#fnote43">43</a>
(“Windows” users should look at the special
<a href="http://www.gnu.org/software/emacs/windows">FAQ</a>.) Emacs is
commonly found on GNU/Linux systems and on *ix systems. It may be
found on other systems when provided by system managers.<a id="revfnote44" href="#fnote44">44</a>

To make use of the didactic production system beyond the syntactic translator a user must have or acquire
the following items of free cross-platform software


<ul>
<li> an ESIS
generating SGML parser such as found in the cross-platform package
<a href="http://www.jclark.com/sp/">SP</a> by James Clark,
which has stood the test of years, or the newer variant
<a href="http://openjade.sourceforge.net/">OpenSP</a>, which
is internationalized, from the OpenJade Team.

</li>
<li> <a href="http://www.cpan.org/">Perl at CPAN</a>.

</li>
<li> a complete TeX system, for which one may look to
<a href="http://www.tug.org">The TeX Users Group (TUG)</a> or
The Comprehensive TeX Archive Network
(<a href="http://www.ctan.org">CTAN</a>).

</li>
<li> xmlwf — a basic utility that is part of the release of
James Clark's <a href="http://expat.sourceforge.net/">expat</a>.

</li>
</ul>


</div>

<div class="subsection">
<h4>7.4.  <a id="SU-7.4"></a>Using the syntactic translator</h4>

This explains how to use the syntactic translator, which is the Emacs Lisp program
contained in the file <a href="../gellmu.el"><kbd>gellmu.el</kbd></a>.


<div class="subsubsection">
<h5>7.4.1.  <a id="SU-7.4.1"></a>Operation in Batch Mode</h5>

For linux and the other *ix a script like <a href="../bin/linux/g2s"><kbd>bin/linux/g2s</kbd></a> will be
adequate if your working directory is the distribution directory<a id="revfnote45" href="#fnote45">45</a>.

<div class="display"><table class="gdisplay"><tbody><tr><td>
Usage: <kbd>g2s  </kbd>stem-name
<kbd>  [ </kbd>function-call<kbd> ]</kbd> </td></tr></tbody></table></div>

For example, if “<kbd>foo.glm</kbd>” is the name of the source file, then
the first argument should be “<kbd>foo</kbd>”. The optional second
argument function-call is the name of the function in the Emacs
Lisp package “<kbd>gellmu.el</kbd>” that is to be used. The function
call defaults to “<kbd>gellmu-trans</kbd>”, which is the correct name for
LaTeX-like usage under the <a href="#ddt">didactic document type</a> (section 5). 

There are also parallel scripts “<kbd>g2h</kbd>” and “<kbd>g2x</kbd>”. 

“<kbd>g2s</kbd>” will byte compile “<kbd>gellmu.el</kbd>” if
“<kbd>gellmu.elc</kbd>” is not present. 

“<kbd>g2h</kbd>” runs the function gellmu-html for the case
where the GELLMU file has been written directly for HTML.
The file <a href="ghtml.glm"><kbd>ghtml.glm</kbd></a> and the derived file <a href="ghtml.html"><kbd>ghtml.html</kbd></a>
are examples. 

“<kbd>g2x</kbd>” runs the function gellmu-xml for the case
where the GELLMU file has been written directly for XML. 

The directory “<kbd>bin/win32</kbd>” contains parallel, though more
complicated, batch files for use in a “DOS” command line
under “Windows”.

</div>

<div class="subsubsection">
<h5>7.4.2.  <a id="SU-7.4.2"></a>Interactive Operation</h5>

Open GNU Emacs interactively on the GELLMU source file. When
finished editing the source, save it but keep Emacs open. Then do

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>M-x load-file gellmu.el</kbd></td></tr></tbody></table></div>

and

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>M-x gellmu-trans</kbd> . </td></tr></tbody></table></div>


(It is better to have byte-compiled “<kbd>gellmu.el</kbd>” and if the
byte-compiled version “<kbd>gellmu.elc</kbd>” is in your Emacs
load-path, then

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>M-x load-library gellmu</kbd></td></tr></tbody></table></div>

is faster.)

The SGML output should come up in a second buffer. Save that buffer
to save the output. 

Make any corrections or changes in the GELLMU source buffer and re-run

<div class="display"><table class="gdisplay"><tbody><tr><td>
<kbd>M-x gellmu-trans</kbd> . </td></tr></tbody></table></div>


As with batch operation the functions gellmu-html and
gellmu-xml, may be handled parallel to gellmu-trans. 

There are a number of other functions besides these three for
obtaining syntactic translation from GELLMU source to SGML. Each of
these is, in fact, a front for calling gellmu-trans with
various combinations of variable settings. There are a great many
user configurable variables in the syntactic translator. Notable
among these for <a href="#regular">regular GELLMU</a> (section 4.1) are (1)
gellmu-parb-nogo and (2) gellmu-autoclose-list.
See the variable documentation text, available interactively when the
GELLMU library is loaded in Emacs with the key combination
qquostrC-h C-h v, for more information. For a list of the names of
all user configurable variables see the variable documentation for
gellmu-public-vars. 

For example, setting gellmu-verblist true causes a sequence of lines
beginning with the line “<kbd>\begin{verbatim}</kbd>” and ending
with the line “<kbd>\end{verbatim}</kbd>” to be considered
verbatim as in LaTeX, i.e., without requiring escaped forms
of special characters, and then to be set as a simple verblist,
which is in most circumstances superior to GELLMU's version of
pre-historic verbatim.<a id="revfnote46" href="#fnote46">46</a>

</div>

<div class="subsubsection">
<h5>7.4.3.  <a id="SU-7.4.3"></a><a id="interrupt"></a>Interrupting the Syntactic
Translator</h5>

Interruption of the GELLMU syntactic translator will be necessary in the event that the
combined use of newcommand, macro, Macro,
and mathsym (advanced mode only) leads to infinite recursive
loops. Users should avoid the use of macro and Macro
unless such use is absolutely necessary since these metacommands
present greater looping risks. 

Inasmuch as there are two ways to invoke the syntactic translator, there are two
different procedures for interrupting it should that be necessary.

<dl>
<dt>
Batch mode invocation</dt>
<dd>This is the case when GNU Emacs is launched
in batch processing mode to run the syntactic translator. To interrupt the syntactic translator in this
case one must interrupt the Emacs process. The author does not
know of any case when Emacs does not respond to standard interrupts.
For example, on linux systems pressing “Control-C”
when the process was launched from a shell provides a standard interrupt.
If the processed was launched in some other way, a normal “<kbd>kill</kbd>”
addressed to the process should have the same effect.
</dd><dt>
Interactive invocation</dt>
<dd>This is the case when the syntactic translator is launched
from within the GNU Emacs editing interface. Use the standard Emacs
function “quit”, accessed with the key “<kbd>C-g</kbd>” (Control-G)
to interrupt the syntactic translator.
</dd></dl>


</div>
</div>

<div class="subsection">
<h4>7.5.  <a id="SU-7.5"></a><a id="usingdps"></a>Using the didactic production system</h4>

<div class="subsubsection">
<h5>7.5.1.  <a id="SU-7.5.1"></a>Staged Design</h5>

The items in the didactic production system are components for use with staged processing.
The document type may be used with any SGML system. Of course, one
may not use a parser that is limited to XML with the SGML version of
the document type. Moreover, if one makes use of features in the
SGML version such as the positional argument and option elements,
then one might want to provide translation to the XML version of the
document type. 

No particular processing system is required for the XML version of
the document type. For example, one might profitably write an
<a href="http://www.w3.org/TR/xslt">XSLT</a> sheet for translation to some
other format and then submit the document and the XSLT sheet
to an XSLT engine such as xt, xsltproc, or
saxon.

</div>

<div class="subsubsection">
<h5>7.5.2.  <a id="SU-7.5.2"></a>Default Staging</h5>

The release includes <a href="../bin/linux/lmkg"><kbd>bin/linux/lmkg</kbd></a> and
<a href="../bin/linux/mmkg"><kbd>bin/linux/mmkg</kbd></a> as example driver scripts for running the
following sequence. (The <a href="../bin/win32"><kbd>bin/win32</kbd></a> directory contains
old driver scripts for the MS Windows command line that might someday
be worth updating.) The behavior of these driver scripts depends
on the way they are called though the specific of this are somewhat
different for <kbd>lmkg</kbd> than for <kbd>mmkg</kbd>. The older
<kbd>lmkg</kbd> scripts do not generate XHTML+MathML at this point they are
provided primarily for backward compatibility. 

The <kbd>mmkg</kbd> scripts by default make XHTML+MathML but not if called by
a name, e.g., via a symbolic link, without the substring “<kbd>mm</kbd>”.
If an <kbd>mmkg</kbd> script is called with a name ending in the string
“<kbd>froms</kbd>” or “<kbd>fromx</kbd>”, then it will take as starting
point, respectively, an SGML, i.e., “<kbd>.sgml</kbd>”, or author-level
XML, i.e., “<kbd>.xml</kbd>”, version of the document. Thus, for
example, <kbd>mmkgfromx</kbd> might be used to operate on a document
that is an author-level XML translation from a non-GELLMU source. 

Caution. These scripts, like all shell scripts, should be
examined for file system locations, system environmental variables,
and other platform-specific and location-specific issues. The user
who introduces a script on a platform should understand the script.
A user who does not understand a script should not attempt to
introduce it on a local platform. 

<a id="flow"></a> Flow in the didactic production system is portrayed in the following diagram:

<div class="display"><table class="gdisplay"><tbody><tr><td>
<img src="gcompst.png" alt="Image file: gcompst.png" />
</td></tr></tbody></table></div>


These are the stages in the didactic production system pipeline:


<ol class="decimal">
<li> Prepare GELLMU source using a text editor.

</li>
<li> Process the source with the syntactic translator to obtain an SGML document under
the didactic document type.

</li>
<li> Use nsgmls to validate the SGML document and obtain an
ESIS for it as output.

</li>
<li> Submit the SGML ESIS as input<a id="revfnote47" href="#fnote47">47</a>
to the Perl
program sgmlspl with the script <a href="../xplaingart.pl"><kbd>xplaingart.pl</kbd></a>
as file argument, obtaining an author-level XML document.

</li>
<li> Use nsgmls to validate the author-level XML document
and then submit its ESIS as input to to sgmlspl
with the script <a href="../xmlgart.pl"><kbd>xmlgart.pl</kbd></a>, obtaining an elaborated
XML document. This document, which is accompanied by several
auxiliary files<a id="revfnote48" href="#fnote48">48</a>,
has things such as sectional unit numbers and cross references
fully resolved so that there will be consistency in these across
the various output formats.

</li>
<li> Use nsgmls to validate the elaborated XML document and
submit its ESIS as input multiply to sgmlspl:

<ol class="lower-alpha">
<li> with the script <a href="../htmlgart.pl"><kbd>htmlgart.pl</kbd></a> to obtain a
classical HTML document that then will be validated if an
HTML validation program is identified in the driver script.


</li>
<li> with the script <a href="../ltxgart.pl"><kbd>ltxgart.pl</kbd></a>
as file argument, obtaining a LaTeX document. The LaTeX
document is then built with latex to make a DVI
file and with pdflatex to make a PDF file.


</li>
<li> for a pipeline using successive runs of sgmlspl with
3 scripts, <a href="../mathcdata.pl"><kbd>mathcdata.pl</kbd></a>, <a href="../mathprep.pl"><kbd>mathprep.pl</kbd></a>,
and <a href="../htmlgart.pl"><kbd>htmlgart.pl</kbd></a> (called in a special way) to make
a XHTML+MathML file that is then checked for XML well-formedness
using xmlwf, checked for certain kinds of MathML
errors using sgmlspl with <a href="../mval.pl"><kbd>mval.pl</kbd></a>, and
validated if a suitable validation program is
identified in the driver script.

</li>
</ol>

</li>
</ol>


</div>

<div class="subsubsection">
<h5>7.5.3.  <a id="SU-7.5.3"></a>Parsing with nsgmls</h5>

The program nsgmls is part of the
<a href="http://www.jclark.com/sp/">SP</a> package, which includes
extensive documentation. Those familiar with it will want to ignore
these hints. 

Since for both the SGML and the XML versions of the didactic document type SP
requires non-default SGML declarations, it is recommended that the user
employ SGML catalogs, one for SGML and another for XML.
The file system location of a catalog is conveyed to nsgmls
as the value of its command line argument immediately following the
argument “-c”. 

Each catalog should contain an SGMLDECL directive that is the
file system location of an SGML declaration. Aside from that a catalog
may contain a number of three string lines of either of the following
forms

<dl>
<dd> PUBLIC  formal-public-identifier  quoted-pathname</dd>
<dd> SYSTEM  quoted-system-identifier  quoted pathname</dd>
</dl>

where the quoted pathname, which may be relative to the location of the
catalog, should for this context in each case be that of a
DTD file. 

It is recommended in each case that nsgmls be run with
arguments “-l” (for propagating line number references) and
“-oempty” (for flagging defined-empty elements). For
processing the XML version of the didactic document type one should additionally use
the argument “-wxml”. 

Additionally, a user may wish to make locally-specific arrangements
for the handling of character sets.

</div>

<div class="subsubsection">
<h5>7.5.4.  <a id="SU-7.5.4"></a>Processing with sgmlspl</h5>

The program sgmlspl is part of David Megginson's
SGMLSPM package. Megginson's extensive documentation for it
may be found in the (December 1995) release found at
<a href="http://www.cpan.org/">CPAN</a>.<a id="revfnote49" href="#fnote49">49</a>

One uses sgmlspl by calling the Perl program sgmlspl
with an ESIS as input and a script as argument. Additional
arguments become arguments for the script. 

Although some operating systems provide a way for dealing with a Perl
program, which is stored in a text file, as an executable object, in
other cases one must explicitly call the Perl engine as a program with
an ESIS as input, the system name of sgmlspl as first
argument, and (the system name of) a script as second argument. In
both cases one will want to arrange, perhaps with an environmental
variable or perhaps with the “-I” argument to the Perl engine,
for the directory containing “<kbd>SGMLS.pm</kbd>” and its supporting
module “<kbd>SGMLS/Output.pm</kbd>” to be in its path array
<kbd>@INC</kbd>.

</div>

<div class="subsubsection">
<h5>7.5.5.  <a id="SU-7.5.5"></a><a id="environmentals"></a>Environmental Variables</h5>

There are a number of environmental variables that affect processing
in the didactic production system. The names all begin with the string “<kbd>GELLMU_</kbd>”.
Of course, the names are case-sensitive. 

Many of these variables are set in the distributed driver scripts.
When that is the case, the distributed driver scripts commonly check
for a previous setting (which may, therefore, be easily placed in a
fronting script that makes a setting and then just calls the
distributed driver). 

Setting environmentals can be difficult in a non-Unix-like
operating system environment. This is one reason why the author
generally recommends that Windows users install GELLMU under
<a href="http://www.cygwin.com/">Cygwin</a>.


<dl>
<dt><kbd>GELLMU_Dir</kbd></dt>
<dd> The top of the directory tree where GELLMU is installed.
</dd>
<dt><kbd>GELLMU_StyleDir</kbd></dt>
<dd> URI or directory location of CSS and XSLT style
sheets that is used by the didactic production system in writing links in XML,
HTML and XHTML+MathML files.
The value usually has a different meaning under the eye of a
web server than in a local file system. A relative URI or
path is usually best. A value like “<kbd>../webstyle</kbd>”
can often be made to work both ways.
</dd>
<dt><kbd>GELLMU_CSSName</kbd></dt>
<dd> Name, relative if given relative syntax, to the value of
<kbd>GELLMU_StyleDir</kbd>, of the CSS stylesheet written by the
didactic production system in HTML and XHTML+MathML files.
</dd>
<dt><kbd>GELLMU_XhtmlSuffix</kbd></dt>
<dd> Suffix given to XHTML or XHTML+MathML files written
by <kbd>htmlgart.pl</kbd>.
</dd>
<dt><kbd>GELLMU_NoUMSS</kbd></dt>
<dd> Value <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>0</mn></math
> or <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>1</mn></math
>: if <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>1</mn></math
>, signals to <kbd>htmlgart.pl</kbd>
that it should not link to W3C's
<a href="http://www.w3.org/Math/XSL/">UMSS</a> XSLT
stylesheets.
</dd>
<dt><kbd>GELLMU_UTF8</kbd></dt>
<dd> Value <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>0</mn></math
> or <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>1</mn></math
>: signals to sgmlspl scripts that
Perl's handling of the UTF-8 text encoding should be invoked.
The meaning is subtly different between Perl versions 5.6
and 5.8.
</dd>
<dt><kbd>GELLMU_Encoding</kbd></dt>
<dd> String value for text encoding that is set by the
<kbd>xplaingart.pl</kbd> in writing author-level XML and by
<kbd>xmlgart.pl</kbd> in writing elaborated XML. (HTML,
XHTML, and XHTML+MathML are always written with the UTF-8
encoding.)
</dd>
<dt><kbd>GELLMU_LaTeXUTF8</kbd></dt>
<dd> Value <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>0</mn></math
> or <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>1</mn></math
>: signals to latex and
pdflatex to expect the UTF-8 encoded text in
their input.
</dd>
<dt><kbd>GELLMU_LaTeXStyle</kbd></dt>
<dd> Pathname for LaTeX stylesheets that latex
and pdflatex should use when such stylesheets are
not properly positioned for TeX system KPSE-based
location. (It's better to use a local or personal
TDS tree.)
</dd>
<dt><kbd>GELLMU_PAPER</kbd></dt>
<dd> String value for the paper used in printing; becomes an
option for the documentclass command in the output
LaTeX file.
</dd>
<dt><kbd>GELLMU_Memoir</kbd></dt>
<dd> Value <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>0</mn></math
> or <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>1</mn></math
>: if <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>1</mn></math
>, use the memoir, rather
than article, documentclass in the output LaTeX file.
</dd>
<dt><kbd>GELLMU_DefaultEmptyEqncenter</kbd></dt>
<dd> Experimental. String value
consisting of a small bit of LaTeX wrapped as a Perl
string to use in tweeking the LaTeX-rendered appearance of
a GELLMU eqnarray (which is rendered in LaTeX using
either align or aligned, depending on
numbering arrangments) in the case of an empty middle cell
(eqncenter). The current default value used in
<kbd>ltxgart.pl</kbd> is the string “<kbd> \qquad </kbd>”. Be
mindful of how such a string can be entered as a literal
string in Perl or as part of an on-the-fly environmental
setting from a command line shell.
</dd>
<dt><kbd>GELLMU_XLink</kbd></dt>
<dd> Value <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>0</mn></math
> or <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>1</mn></math
>. How to handle links in MathML output
when writing XHTML+MathML. Such links, which are currently
illegal inside XHTML+MathML math zones, are confined to
<kbd>\text{...}</kbd> areas in GELLMU. If the value is <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mn>1</mn></math
>, use
XLink; otherwise, switch into the HTML namespace and
write an HTML anchor. (Firefox handles both,
while more of the other browsers seem to choke on the
namespace switch than choke on the necessarily cumbersome
use of XLink.)
</dd>
<dt><kbd>GELLMU_OriginLabel</kbd></dt>
<dd> Name for an automatic label key, chiefly of occasional
value for HTML and XHTML+MathML outputs, that, when this
variable is present in the environment, places a link target,
with id the value of this variable, at the top of the document.
</dd>
</dl>


</div>
</div>
</div>

<div class="section">
<h3>Appendix A.  <a id="SU-8"></a><a id="KEY-5"></a><a id="archive"></a>The GELLMU Archive</h3>

The GELLMU Archive is the web site
<a href="http://www.albany.edu/~hammond/gellmu/"><kbd>http://www.albany.edu/~hammond/gellmu/</kbd></a>. 

It is the source for late breaking information about GELLMU.
Among other things, it houses a largely uncommented
<a href="http://www.albany.edu/~hammond/gellmu/examples">archive of examples</a>. This is provided
in the belief that the study of examples is one of the quickest
ways to learn a markup language. 

Of course, this document, which is furnished with the release,
is also an example. 

Another item, also an example, that is housed in the archive
is <a href="http://www.albany.edu/~hammond/gellmu/examples/gfaq.html">The GELLMU FAQ</a>.

</div>

<div class="section">
<h3>Appendix B.  <a id="SU-9"></a><a id="KEY-6"></a><a id="release"></a>Release Notes</h3>

This version of the manual was prepared for release 0.8.5 in
July 2007. The <a href="#materials">GELLMU materials</a> (section 7.2) consist of:


<ol class="decimal">
<li> The manual, which is this document.

</li>
<li> The GELLMU syntactic translator, a Emacs Lisp program, which is the only
item of software required for those who simply wish to use GELLMU
markup for the conscious preparation of HTML documents or documents
under some other classical SGML or XML document type for which the
user is otherwise equipped.

</li>
<li> The GELLMU didactic production system, which consists of
an SGML document type called article, an XML document type
also called article, and three separate collections of Perl
functions for the well-known Perl SGML processing framework
sgmlspl by <a href="http://www.megginson.com/">David Megginson</a>.
A very slightly modified version of Megginson's Perl library
SGMLSpm that provides a method for detecting defined-empty
SGML elements, as flagged in an SGML parse stream in ESIS
format, is included as part of the didactic production system.
Since it is by size 60% of the software content of the
Megginson package on <a href="http://www.cpan.org/">CPAN</a>, the rest of the
package, licensed under the GNU
<a href="http://www.gnu.org/copyleft/gpl.html">General Public License</a>
is distributed with the didactic production system as well, though without its
documentation. The distribution includes 7 scripts for use with
sgmlspl in the didactic production system pipeline. For more
on this see <a href="#usingdps">“Using the didactic production system”</a> (section 7.5).

</li>
</ol>



<div class="subsection">
<h4>B.1.  <a id="SU-9.1"></a>Comments on the Syntactic Translator</h4>

The GELLMU syntactic translator is more mature than the other components. The following
comments pertain to it.


<dl>
<dt>internationalization</dt>
<dd>

Internationalization has a considerable and evolving
level of support in Emacs. The concept is that an author resides in
a locale. When the author enters a character from a locale, it gives
rise in Emacs to a somewhat complicated multibyte entity that can have
“properties”. Particularly relevant variables in Emacs
are: <kbd>coding-system-for-write</kbd> and
<kbd>buffer-file-coding-system</kbd>. GELLMU provides the user
variable <kbd>gellmu-sgml-default-coding</kbd>, which should be properly
coordinated via driver script settings with one's SGML parser.

</dd>
<dt>inclusions</dt>
<dd>

It is not actually a limitation that a GELLMU source file cannot
be included in another. The primary reason is that one should
make use of the inclusion mechanism of SGML. For that one needs
to define the included pieces as entities in the direct internal
subset <a id="revfnote50" href="#fnote50">50</a>
of the source file and then reference each as an entity, e.g.,
“<kbd>&sect2;</kbd>” at the appropriate location in the source
file where it is to be included. Because the inclusion happens
at the SGML level there are two points to observe:

<ol class="decimal">
<li> Macro information is local to each source file. 
</li>
<li> The situation is optimal for the location of validation
errors provided that one's parser reports such errors by
filename and line number since the syntactic translator
provides line number alignment between source and generated
SGML. 
</li>
</ol>


A second reason is that source inclusion would disturb
line number alignment between source and SGML output. This
is important for the interpretation of SGML validation error
messages. Such validation is considered routine, and plays an
important role in detecting an author's mistakes. Some author errors
are diagnosed in the syntactic translator. 

A third reason, which at the same time might be considered also
a disadvantage, is that all of GELLMU's macro facilities are
local to each source file. This adds both robustness and flexibility
at the price of the inconvenience of physical inclusion of common
macro definitions.

</dd>
<dt>variable management</dt>
<dd>

This refers to the management of user variables in the syntactic
translator. These are Elisp variables. One who is familiar with
Elisp should be able to provide values in batch mode without
making changes in the Elisp source.<a id="revfnote51" href="#fnote51">51</a>
Setting values interactively in the Emacs editing interface can be
done easily using “<kbd>M-x set-variable</kbd>”. 

With a future release it is likely that additionally a user resource
file for custom variable settings without the need for writing Elisp
code will be provided.

</dd>
<dt>Bugs</dt>
<dd>

No serious existing problem is known in the GELLMU syntactic translator at the time of this
release. Of course, as stated in source code comments, there is no
warranty of any kind. Please report bugs to the author:
<a href="mailto:[email protected]"><kbd>[email protected]</kbd></a>.


<ul>
<li> Reserved element names.
The GELLMU syntactic translator reserves for its own internal use all SGML or XML element
names in which the first numeric character in the range
“0–9” is the character “0”.

</li>
<li> Limitation on braces in macros.
Unbalanced braces are not permitted in either the name or the value
field of any form of macro metacommand.

</li>
<li> First cell limitation.
In the LaTeX-like emulation of an array or tabular
environment the first cell in each row must have something other than
whitespace. Of course, sometimes no content is wanted, and then
<kbd>\empty</kbd> (for nil markup, not to be confused with the mathematical
<kbd>\emptyset</kbd>) is one way to handle it, but this author usually uses
something that is mostly inconsequential like “<kbd>~</kbd>” or
“<kbd>\,</kbd>”. Another way to handle it is to invoke the names
of the SGML elements, i.e., <kbd>\firstcell{}</kbd> for tabular or
<kbd>\firstacell{}</kbd> for array.

</li>
<li> Concept of advanced GELLMU immature.
Inasmuch as didactic article is the only document type for
which the idea of advanced GELLMU has been implemented, the general
concept of advanced GELLMU is not fully developed in the GELLMU syntactic translator.
Basic GELLMU is characterized in the GELLMU syntactic translator by the evaluation of
the Boolean variable gellmu-straight-sgml to “true”.
This automatically make the Boolean variable
gellmu-regular-sgml true.
Full LaTeX-like support for the didactic production system is realized only by both
of these Booleans being false. Thus, advanced GELLMU will
need to evolve in the space in between, probably after the
introduction of further such Boolean variables, some public and
some private. This technique will make it possible for the
code to continue performing as now when the variable
gellmu-straight-sgml, the flag for basic GELLMU, is true
and also when both of these flags are false.

</li>
<li> Reserved strings.
The strings “<kbd><<</kbd>” and “<kbd>>></kbd>” have been reserved
as future notation for mathematical objects. Although it might seem
at first glance that this type of short hand has no place apart from
the fully LaTeX-like environment of the GELLMU syntactic translator in the context of the didactic production system, in
which they have not yet been used, it is actually not so clear that
one could not make sensible use of such notation in the context of
“XHTML plus MathML” under advanced GELLMU along with
other features such as blank lines for new paragraphs and many other
mathematical shortcuts. It awaits the further development of advanced
GELLMU, and reserving this notation is necessary to ensure backward
compatibility.

Consequently, for example, entering “<kbd><<a>></kbd>” is
problematical, because only the first “<kbd><</kbd>” or “<kbd>></kbd>”
will be converted to something appropriate. In basic mode
“<kbd>&lt;</kbd>” and “<kbd>&gt;</kbd>” are one-step ways of
circumventing this when these entities are available, which is
guaranteed for any form of HTML as well as for any form of XML. In
the didactic production system one should use “<kbd>\ltc;</kbd>” and
“<kbd>\gtc;</kbd>”. For other cases the one-step circumvention is
to use entity references to the numeric character codes, e.g., in
ASCII “<kbd>&#3C;</kbd>” and “<kbd>&#3E;</kbd>”, and for
convenience these may be brought up as macros, perhaps
“<kbd>\lt</kbd>” and “<kbd>\gt</kbd>”.

</li>
</ul>


</dd>
</dl>


</div>

<div class="subsection">
<h4>B.2.  <a id="SU-9.2"></a>Comments on the Didactic Production System</h4>

The didactic production system is to be understood as a potential base for development.
As such it is not intended ever to offer everything that might
be imagined. The following comments pertain to it.


<div class="subsubsection">
<h5>B.2.1.  <a id="SU-9.2.1"></a>Internationalization</h5>

Internationalization has been a concern of the project. It is
possible, for example, to use the ISO-Latin-1
character ‘é’ in the name of an element. The
didactic article document type offers, for example, an element
étale, which is a style, parallel to bold.
Use of the character ‘é’ as a raw word character
data with the didactic production system is less robust than the more careful
“<kbd>\acute{e}</kbd>”<a id="revfnote52" href="#fnote52">52</a>
construction, which is desirable for translation of article
to formats that do not support latin1. For that matter, the
exact extent of LaTeX's support of latin1 is a bit tricky, and
the whole matter of internationalization is currently under
review in the LaTeX project.<a id="revfnote53" href="#fnote53">53</a>

</div>

<div class="subsubsection">
<h5>B.2.2.  <a id="SU-9.2.2"></a><a id="doctypes"></a>Document Type Definitions</h5>

Currently the project has one SGML document type definition
and two XML document type definitions. Files under the
various document types are suffixed as follows:

<div class="display"><table class="gdisplay"><tbody><tr><td>
<table><tbody>
<tr><td align="left">First stage SGML</td><td align="left"><kbd>.sgml</kbd></td></tr
><tr><td align="left">Author Level XML</td><td align="left"><kbd>.xml</kbd></td></tr
><tr><td align="left">Elaborated XML</td><td align="left"><kbd>.exml</kbd></td></tr
></tbody></table>
</td></tr></tbody></table></div>


Additionally, in the three steps of processing to generate an
XHTML+MathML file from an elaborated XML file there are two intermediate
XML files generated, the first with suffix “<kbd>.yml</kbd>”, which
lives under the document type definition for an elaborated XML
document, and the second with suffix “<kbd>.zml</kbd>”, an XML file
for which there is no extant formal document type
definition.<a id="revfnote54" href="#fnote54">54</a>

The author-level XML document type is formalized by the
DTD "axgellmu.dtd", while the elaborated XML document
type is formalized by a modification that is found in the DTD
"uxgellmu.dtd". (The latter was the only XML document type
used with the regular GELLMU production stream prior to
October, 2006.)

The document type represented by "uxgellmu.dtd" is now called the
elaborated XML document type. 

The author-level XML document type is suitable as a translation
target from other markups. The elaborated XML document type
should not be used as a translation target other than from the
GELLMU author-level XML document type. 

All document type definitions are available under the UTF-8
text encoding. The two older document type definitions will continue
to exist for a while under the Latin-1 (ISO-8859-1) text
encoding. The text encoding of a so-called DTD file (not
quite the same thing as a document type definition) is significant
in regard to the names of SGML/XML entities and
elements rather than in regard to document instances which might
be processed. The names of the DTD files are:
<a id="dtdfiles"></a>

<div class="display"><table class="gdisplay"><tbody><tr><td>
<table><tbody>
<tr class="bruled"><td class="rruled" align="left"> </td><td class="lruled" align="center">Latin-1</td><td align="center">UTF-8</td></tr
><tr class="truled"><td class="rruled" align="left">First stage SGML</td><td class="lruled" align="center"><kbd>gellmu.dtd</kbd></td><td align="center"><kbd>ugellmu.dtd</kbd></td></tr
><tr><td class="rruled" align="left">Author Level XML</td><td class="lruled" align="center"> </td><td align="center"><kbd>axgellmu.dtd</kbd></td></tr
><tr><td class="rruled" align="left">Elaborated XML</td><td class="lruled" align="center"><kbd>xgellmu.dtd</kbd></td><td align="center"><kbd>uxgellmu.dtd</kbd></td></tr
></tbody></table>
</td></tr></tbody></table></div>


</div>

<div class="subsubsection">
<h5>B.2.3.  <a id="SU-9.2.3"></a>Translation to XML</h5>

Presently the author-level XML files link to a CSS stylesheet that
provides primitive rendering. One could go further in this direction,
but the rendering of mathematics will be limited without more development
in that direction of CSS.

</div>

<div class="subsubsection">
<h5>B.2.4.  <a id="SU-9.2.4"></a>Translation to HTML</h5>
<dl>
<dt>
Math in classic HTML</dt>
<dd>The classic HTML output does not use graphic images for mathematical
zones in the manner of programs like latex2html. Instead it
uses pseudo-TeX notation for math.
There are a
number of reasons:
<ol class="decimal">
<li> Well typeset mathematics is available in the modern form of
HTML that is more precisely called XHTML+MathML. 
</li>
<li> Graphical images completely block accessibility in the
sense of the World Wide Web Consortium's
<a href="http://www.w3.org/WAI/">Web Accesibility Initiative</a>. 
</li>
<li> The present classical HTML output files may be deciphered
in terminal window browsers. 
</li>
<li> The present classical HTML output files may be “dumped” to
plain text using a program such as lynx or w3m
for various sometimes useful purposes. 
</li>
</ol>

</dd><dt>
Style.</dt>
<dd>HTML and XHTML+MathML made with the didactic production system now rely on CSS, even, for
some things, level 2 CSS.
</dd></dl>
</div>

<div class="subsubsection">
<h5>B.2.5.  <a id="SU-9.2.5"></a>Translation to LaTeX</h5>

This translator writes LaTeX2E. A number of packages, including
graphicx, amsmath, amssymb, amsfonts,
bm, url (not hyperref for the standard track
where the focus is on printed output), and inputenc for UTF-8
(which may be needed even if the GELLMU source or, otherwise, the
author-level XML source is not UTF-8 encoded).
Apart from current font availability issues, the author would have
preferred to invoke the T1 font encoding. 

Even though GELLMU source uses the names equation and
eqnarray, in the LaTeX formatting amsmath constructions
are used. 

A small modification of this translator can be used to write
Adobe's Portable Document Format (PDF) with pages sized for screens
rather than for paper.

</div>

<div class="subsubsection">
<h5>B.2.6.  <a id="SU-9.2.6"></a>Future Plans</h5>

This is a very limited list.

<dl>
<dt>A literate document type definition.</dt>
<dd>

Capable of spawning not only the 5 DTD's but type definitions
under other mechanisms such as, for example, RelaxNG.

</dd>
<dt>Mathematical Semantics</dt>
<dd>

Provision for optional semantic tightening sufficient for authors
wishing to be able to export mathematical markup into computer algebra
systems.

</dd>
</dl>


</div>
</div>
</div>
<hr />
<h3>Footnotes</h3>
<ol>
<li><a id="fnote1" href="#revfnote1">*</a> The syntactic translator does, however, have some facilities for
classifying the names in a list in regard to common syntactic
behavior. See, in particular, the Elisp variables
gellmu-autoclose-list and gellmu-parb-hold, both
of which are not significant in basic GELLMU.</li>
<li><a id="fnote2" href="#revfnote2">*</a> With several minor exceptions, one related to the direct writing of
SGML attributes (which cannot contain markup and which do not have
many parallels in LaTeX) and another related to the way of escaping
the character ‘<kbd>\</kbd>’, everything about basic mode also
applies to advanced mode.</li>
<li><a id="fnote3" href="#revfnote3">*</a> There is a way, with the setting of several
variables for the syntactic translator in advanced mode, to have blank lines begin
new paragraphs in basic input for HTML</li>
<li><a id="fnote4" href="#revfnote4">*</a> This means that it is a relatively slow form of processing, but
the author believes that it is a good match for the intuitive
expectations of most LaTeX users. </li>
<li><a id="fnote5" href="#revfnote5">*</a> In a future release an alternative metacommand
called frontcommand may be provided which could be used, for
example, if one wishes to have a macro name of some kind match the
name of an actual SGML element. </li>
<li><a id="fnote6" href="#revfnote6">*</a> In the prototype production system based on
the didactic article document type the output from each
stage is available for examination and, where necessary, intervention.
However, such use of intervention is intended only for temporary
expedient use while a GELLMU system is being designed or enhanced.
As with LaTeX, enhancement is an ongoing process. </li>
<li><a id="fnote7" href="#revfnote7">*</a> In handling GELLMU source markup one could provide
a more elaborate processor that can be configured to know for each
such command the list of names for its positional arguments and
options. It was decided that this goes somewhat beyond syntactic
handling but that the question of whether a list of arguments and options
corresponds to sole content might be regarded as a syntactic matter. </li>
<li><a id="fnote8" href="#revfnote8">*</a> Its use is optionally permitted in basic mode as well. </li>
<li><a id="fnote9" href="#revfnote9">*</a> Indeed, LaTeX usage allows markup in options, but (element level)
markup is not permitted in SGML attributes. Note, however, that
in the didactic document type the SGML content model for an option is more restrictive
than that for an argument. Also in the didactic document type some options, such as
that for anch, which is described later in this section, are
practically required. </li>
<li><a id="fnote10" href="#revfnote10">*</a> To say seldom is not to say not. Two important
instances in the didactic production system are the series attribute for the
label command, which stands in, to the extent possible, for the
notion of counter in LaTeX, and the type attribute for
the series command, which provides emulation of counter
conversion from, say, number values to letter values. </li>
<li><a id="fnote11" href="#revfnote11">*</a> In the XML version of article the option becomes the element
anchref and the anchored text becomes the element anchv.
One may use these names directly in GELLMU source, but option/argument
notation is more familiar and more succinct. </li>
<li><a id="fnote12" href="#revfnote12">*</a> There was no list
of this type in early pre-release versions of the syntactic translator. </li>
<li><a id="fnote13" href="#revfnote13">*</a> The LaTeX concept of document class has only a loose correspondence
with the SGML concept of document type. </li>
<li><a id="fnote14" href="#revfnote14">*</a> It is not inconceivable that at some future point conscious writing
for some XML document types using LaTeX-like markup might be
subsumed in the LaTeX project, but in saying this, the author is
neither predicting it nor assessing the merits of the idea. He has no
affiliation with the LaTeX project other than as a user. </li>
<li><a id="fnote15" href="#revfnote15">*</a> Strict discussion of an SGML document type would not allow use of the
word handled. In this instance a coordinated pair of document
types is being described, one SGML and the other an XML translation.
For most purposes the SGML document type is the richer of the two.
However, because of its use of a handful of generic elements (in its
reserved namespace consisting of names that contain ‘<kbd>0</kbd>’ (zero)
as first numeric character) for modeling certain convenience features
of LaTeX, it is possible for a correct translation of a valid SGML
article to yield an XML version that fails validation because the
content models of the generic elements are necessarily loose. </li>
<li><a id="fnote16" href="#revfnote16">*</a> The variable
gellmu-xml-strict is by default unset in advanced mode. </li>
<li><a id="fnote17" href="#revfnote17">*</a> The correct LaTeX markup is “<kbd>\LaTeX{} document</kbd>”. In the didactic production system the
name of LaTeX is “latex”, which is a defined-empty
element, that for the SGML version of article may be marked up
safely either as “<kbd>\latex;</kbd>” or as “<kbd>\latex{}</kbd>”. </li>
<li><a id="fnote18" href="#revfnote18">*</a> In math ‘<kbd>[</kbd>’ sometimes needs to be escaped to prevent confusion
between its markup use and its ordinary use in an instance such as
the markup for <math xmlns="http://www.w3.org/1998/Math/MathML" mode="inline"
><mi mathvariant="double-struck" mathcolor="#b00">Z</mi
><mo stretchy="true">[</mo><mi>t</mi><mo stretchy="true">]</mo></math
>. The syntactic translator would need to know
vocabulary — at least the argument/option pattern for
mathbb — in order to elude the syntactic ambiguity. </li>
<li><a id="fnote19" href="#revfnote19">*</a> “<kbd>\~</kbd>” is an example of a markup string that is defined in LaTeX (for
an accent) that is not defined in the didactic document type. A LaTeX user may recover
a prior markup habit of this type using newcommand possibly in
combination with macro. For more information see the
<a href="#accents">discussion of accents</a> (section 5.8). </li>
<li><a id="fnote20" href="#revfnote20">*</a> It is possible to merge the inline math and tmath zones
at any level of processing beyond the syntactic translator. These are indeed the same
in LaTeX, but the syntactic translator resists the temptation here to
go beyond syntax and merge them. With the didactic article
document type the formatting to LaTeX inserts the LaTeX markup
“<kbd>\,</kbd>” for a small horizontal space before and after
math, but not before and after tmath. </li>
<li><a id="fnote21" href="#revfnote21">*</a> The syntactic translator simply outputs the SGML defined-empty element
brk0, which belongs to its reserved name space. The dual use of
brk0 involves some SGML chicanery that is resolved during translation
to the XML version of the article document type,
where tabular is converted to table and non-tabular use of
brk0 is converted to brk. See also the handling of
array, which is different even though the source markup, as in
LaTeX is similar. </li>
<li><a id="fnote22" href="#revfnote22">*</a> Alternate forms “<kbd>\aos;</kbd>”, “<kbd>\aoq;</kbd>”, “<kbd>\aoe;</kbd>” of sentence ending
punctuation are provided that may be used following inline mathematical
markup at the end of a sentence. Similarly, “<kbd>\aoc;</kbd>” is an alternate
form for a comma. </li>
<li><a id="fnote23" href="#revfnote23">*</a> Or one
could use:
<dl class="verblist">
<dd><kbd>
\Section{\sectiontitle{Some...}</kbd></dd>
<dd><kbd>
\para A para...  . . .}</kbd></dd>
</dl>

instead of using the environment-like
begin/end construction. </li>
<li><a id="fnote24" href="#revfnote24">*</a> In fact, classical SGML document types are often
even more elaborate than this.</li>
<li><a id="fnote25" href="#revfnote25">*</a> Caveats:
<dl>
<dd> No document type definition under SGML is actually a complete
language definition. A document type definition describes a document
markup structurally; in particular, it does not provide definition
for legal “field” values. </dd>
<dd> While the GELLMU syntactic translator is now considered as
“alpha” software, the document type and the accompanying
translators, which constitute the didactic production system are
developmental. These materials have some support for obsolete
practice and also contain sketch sections that are not fully robust. </dd>
</dl>
</li>
<li><a id="fnote26" href="#revfnote26">*</a> It is recommended that the characters in label key strings be
restricted to lower case ASCII letters, the digits 0–9, and
possibly the character ‘<kbd>-</kbd>’ or the character ‘<kbd>.</kbd>’ for
maximal inter-operability with current and future formattings.
For example, the ‘<kbd>_</kbd>’ is problematical in this context. </li>
<li><a id="fnote27" href="#revfnote27">*</a> Although one could provide SGML modeling for LaTeX's
counters, it would not be very much along the lines of main track
SGML or XML document types. </li>
<li><a id="fnote28" href="#revfnote28">*</a> The value strings may contain simple markup such as, for example,
“<kbd>\tld;</kbd>” to provide robust multiple output processing of
‘<kbd>~</kbd>’ whereas an attribute option may not contain markup. </li>
<li><a id="fnote29" href="#revfnote29">*</a> A klabel is a
“visible key” label.</li>
<li><a id="fnote30" href="#revfnote30">*</a> It may be left empty, but it must be present.
</li>
<li><a id="fnote31" href="#revfnote31">*</a> The presence of sopt
does not cause a table of contents to be produced automatically.
For that one uses “<kbd>\tableofcontents</kbd>”. Moreover,
the presence of sopt should have no effect upon a manually
constructed “<kbd>\TableOfContents</kbd>”.</li>
<li><a id="fnote32" href="#revfnote32">*</a> The didactic production system offers a way to furnish a formally empty string, which is an
empty element called empty in the document type for use in
places such as the the table of contents option of a sectional unit,
where it is not otherwise possible to distinguish after parsing whether
deliberately empty content was specified by the author.
That is, the markup “<kbd>\sopt{}</kbd>” furnishes an empty
string which, in turn, signals “no sopt”, while
“<kbd>\sopt{\empty;}</kbd>” indicates that empty content
was specified for sopt. </li>
<li><a id="fnote33" href="#revfnote33">*</a> When editing for HTML one may, of course use HTML's pre,
which stands for “pre-formatted text”</li>
<li><a id="fnote34" href="#revfnote34">*</a> With a sufficiently long list of output format candidates each of the
33 non-alphanumeric printable ASCII characters is unsafe.
However, one might use an external character-to-string conversion
program to prepare a large amount of verbatim material for inclusion
inside the simplistic verbatim command in GELLMU source. </li>
<li><a id="fnote35" href="#revfnote35">*</a> To export this procedure for general advanced mode usage, all
of the names used need to be made user-configurable. </li>
<li><a id="fnote36" href="#revfnote36">*</a> Familiar short forms
may be introduced by a user using the macro facility.</li>
<li><a id="fnote37" href="#revfnote37">*</a> For the
third method one's GELLMU driver script must provide appropriately
for the text encoding of the source file.</li>
<li><a id="fnote38" href="#revfnote38">*</a> This meaning of scale differs
from the meaning of scale with includegraphics under
LaTeX's graphicx package. New controls of this type
may be introduced in a future version.</li>
<li><a id="fnote39" href="#revfnote39">*</a> Note that the use of lbalbr in this instance is insufficiently
semantic for translation to content MathML while it is meaningful
for translation to presentation MathML. Adequate enhancement might
be had by providing <kbd>mml="cases"</kbd> (using a name from amsmath)
as an attribute for lbalbr with this example. </li>
<li><a id="fnote40" href="#revfnote40">*</a> There is also a default counter that is used when no label series name
is present. That counter simply is the position of the underlying
assertion in the list of all assertions. </li>
<li><a id="fnote41" href="#revfnote41">*</a> However, a declared math symbol may be invoked in
a newcommand that takes arguments. </li>
<li><a id="fnote42" href="#revfnote42">*</a> Such unattached braces in GELLMU markup lead to an lg0 tag in
the output of the syntactic translator that is translated to an
lgg tag in the XML version of the didactic document type. </li>
<li><a id="fnote43" href="#revfnote43">*</a> Version 20 or later should be adequate. Although the author began
this project using version 19, he is no longer able to run tests
with that version.</li>
<li><a id="fnote44" href="#revfnote44">*</a> It is an embarrassment of the business world in the years since 1985
that many business computing installations do not provide general
purpose cross-platform programming systems despite the widespread
availability of excellent free robust systems such as Emacs (for
Lisp), gcc (for C), and Perl. This new phenomenon
apparently arises not so much from lack of organizational interest but
from the fact that the responsibility for maintenance cannot be passed
beyond the local system manager to a vendor. </li>
<li><a id="fnote45" href="#revfnote45">*</a> None of the enclosed scripts either for linux or for win32 should be used
without prior examination and verification for suitability. </li>
<li><a id="fnote46" href="#revfnote46">*</a> The main reasons that this version is not the default with a call to
gellmu-trans are:
<ol class="decimal">
<li> It breaks the paradigm under which a GELLMU command name is the
name of an SGML element. 
</li>
<li> It breaks backward compatibility with earlier versions of the
syntactic translator, i.e., breaks older documents. 
</li>
<li> It is felt that the user invoking verblist this way
should be aware of what is being done. 
</li>
</ol>

Note that direct invocation of verblist requires escaping
special characters. Thus, using the function call
gellmu-verblist converts the name verbatim from a
command name to a meta-command name.</li>
<li><a id="fnote47" href="#revfnote47">*</a> Specifically, this mention of “input” refers to
what is called “standard input” in a command line
situation. There may be a challenge here on platforms that do
not provide a command line. </li>
<li><a id="fnote48" href="#revfnote48">*</a> Formally, two of these auxiliary files are considered part of the
elaborated XML document. </li>
<li><a id="fnote49" href="#revfnote49">*</a> At the time of this release
there was discussion in the UseNet newsgroup
<a href="news:comp.text.sgml"><kbd>news:comp.text.sgml</kbd></a> about a proposed revision of
SGMLSPM by another party. The code for “<kbd>SGMLS.pm</kbd>”
included in this GELLMU release contains a very small modification
of Megginson's 1995 release. </li>
<li><a id="fnote50" href="#revfnote50">*</a> The direct internal subset is the content of the optional argument of
the documenttype metacommand that follows its required argument.
It should be noted in the didactic production system that the direct internal
subset cannot be propagated to the XML form of article
because it is digested by any standard SGML parser and, hence,
by any translation based on a standard parsing. Thus,
any pieces are merged in the XML form of an article although
the translator <kbd>xmlgart</kbd> might be modified to
construct an internal declaration subset there and provide
partitioning of the XML version among filesystem pieces based
on document structure. </li>
<li><a id="fnote51" href="#revfnote51">*</a> Please observe the rules of the LaTeX project regarding filenames
as well as the license rules of the GNU General Public License
if you wish to distribute a modified version of the Elisp
source. Alternatively, the author is always interested in learning
of suggestions for change.</li>
<li><a id="fnote52" href="#revfnote52">*</a> The corresponding usage in LaTeX would be “<kbd>\'e</kbd>”;
this could be brought into GELLMU source using \macro,
but it must be resolved to a name in the output of the GELLMU syntactic translator where
everything that is markup needs a name. Rather than using a
general container acute, the document type could have provided
a name for the specific character. </li>
<li><a id="fnote53" href="#revfnote53">*</a> Alternatively LaTeX source can be submitted to the program
lambda which is the LaTeX format for the program
omega that is now under development as a substitute for
Knuth's TeX, the program, with internationalization as a stated
goal.</li>
<li><a id="fnote54" href="#revfnote54">*</a> There is no formal document type definition
for a “<kbd>.zml</kbd>” file because such a file is endowed via XML
attributes with information about tree structure for
mathematical zones.</li>
</ol>
</body>
</html>