Guide to LaTeX (4th Edition) (Tools and Techniques

480 Appendix E. L AT E X and World Wide Web
\usepackage[xhtml,docbook]{tex4ht} for XML, DocBook output
\usepackage[xhtml,tei]{tex4ht} for XML, TEI output
One might ask why does the author not write an XML file directly as
the source document? First, one might very well want to convert older
documents recorded in L AT E X to XML. Secondly, one might find it simpler
to write in L AT E X (not everyone agrees) since no one would write an XML
file by hand (everyone agrees) but would rely on some application to do it
behind the scenes. Certainly L AT E X source text is easier to read, even when
intersperse with commands, than an XML file.
E.2.2 MathML and L AT E X
One of the strengths of T E X and thus L AT E X over other text processing
systems is the ability to handle mathematics in a way that is acceptable to
mathematicians. HTML has never been able to even begin to compete in
this area. The only way conversion programs like L AT E X2HTML and T E X4ht
can render equations like that in Figure E.1 is to convert it to an image
file. This is hardly a satisfactory solution.
The MathML project attempts to define an XML language to encode
mathematics. We refer to chapter 8 of the L AT E X Web Companion (Goossens
and Rahtz, 1999) for a description. T E X4ht can produce output in MathML
by specifying
\usepackage[xhtml,mathml]{tex4ht}
Symbols that do not exists in the browser fonts will still be converted to
image files, but instructions are inserted to carry out the placement for
fractions and superscripts and subscripts. Unfortunately, most browsers
do not recognize MathML (yet). Again, once this becomes established
there will be a standard for recording and exchanging documents with
complex mathematics.
E.2.3 Rendering XML with T E X/L AT E X
Another role that L AT E X, or more properly the T E X program, can play in the
XML world, is to translate it to a form that can be viewed or printed as a
finished document. This is known as rendering.
David Carlisle has written macros in a file xmltex.tex to act as an
XML parser for output in T E X or L AT E X. Sebastian Rahtz has written an
additional macro package PassiveT E X, to incorporate an XSL style sheet
for the TEI DTD into xmltex. With this combination, one can produce DVI
or PDF output from a TEI-coded XML file.
There are a number of ways of going about this. The simplest is to
write a ‘wrapper’ file for processing document.xml as