\documenttype{article}
\newcommand{\gellmu}{\abbr{GELLMU}}
\newcommand{\sgml}{\abbr{SGML}}
\newcommand{\xml}{\abbr{XML}}
\newcommand{\ic}[2][]{%
\label[:series="axf1"]{#1}(\ref{\popkey}) #2 (suffix \quostr{.#1})%
}
\surtitle{The \gellmu Archive}
\title{About the XML Files Found Here}

\begin{document}

The files in this directory are all examples under the didactic document
type that is called \emph{article}.

From early days of the project until mid 2006 the translator that
converted the \sgml form of an \emph{article} to the (only) \xml form
of \emph{article} automatically generated section numbers, tables of
contents, and cross-referencing information.

Since mid 2006, this stage of the standard pipeline has been split in
two, and there are now two \xml versions of \emph{article}.  The one
produced directly from \sgml (with suffix \qquostr{.xml}) is
author-level and very nearly equivalent to original source.  It
resides under a strict document type definition for the \xml version
of \emph{article} that may be regarded as suitable for authors who
wish to write \emph{article} originally as \xml source.  With the new
standard pipeline these \xml document instances qualify as
``stand-alone'' \xml documents.

The second \xml form of \emph{article} (with suffix \qquostr{.exml})
is very nearly equivalent to what was previously the only \xml form of
\emph{article} in the production system.  For maximum efficiency in
subsequent generation of end formats the translator producing the
second \xml form simultaneously produces various auxiliary files
containing \ic{xet}{\xml entity definitions}\footnote{
Some of the entity definitions may be superfluous, but they cause no harm.
(There is more than one conceivable way to generate the \xml version of
an article.)
},
\ic{xlb}{label information}, and \ic{xcn}{a table of contents} as
appropriate.

The items (\ref{xet}) and (\ref{xcn}) represent included entities in the
second \xml version of an \emph{article} and, therefore, must be present in
order to produce conforming \xml.  This means that the second \xml form
of an \emph{article} does not qualify as a ``stand-alone'' \xml instance.
The current formatters for the \abbr{HTML} and \latex; targets
make use of item (\ref{xlb}).

In early 2002, motivated by \abbr{CSS} handling in the browser
\softw{Opera~6}, the author began very tentatively building a
\abbr{CSS} style sheet for browser-based rendering of the XML version
of the \abbr{GELLMU} \emph{article} document type.  The \abbr{CSS}
sheet remains very much under construction, and, at best, \abbr{CSS} is
a cruder rendering vehicle for arbitrary XML tag vocabularies than a
finely honed translation to standard \abbr{HTML} or \abbr{XHTML} with
appropriate use of \abbr{CSS} styling.

In general, there is an expectation that a web browser with \xml
capability will render an \xml document that is accompanied by a
\abbr{CSS} style sheet, but such browsers, as a general rule,
should not be expected to handle document instances except when
``stand-alone''.

In particular, the first \xml form of an \emph{article} is the one
that should be considered most suitable for \abbr{CSS}-styled
rendering.

\end{document}