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Why the LATEX community should care except insofar as it involves CSS-only rendering of about SGML most of LATEX math. My GELLMU Project, found at my university William F. Hammond website, albany.edu/~hammond/gellmu, as well at Abstract CTAN (ctan.org/pkg/gellmu) provides a didactic model for the use of a LATEX profile. Given that the universal format-to-format translator A Pandoc is coming of age, LTEX authors are tempted 1.2 A side remark on accessibility to think that whatever LATEX they write can quickly be translated without worry to whatever other format In reference to the first of Ross Moore’s talks at this may be required. meeting, I want to suggest that HTML 5 [3], with Of course, that is not exactly true, but the use Unicode text and MathML for math, obtained from a LAT X profile can rather easily be made accessible of an XML profile of LATEX can make it exactly true. E for those with vision impairment. However, an SGML profile of LATEX can provide closer emulation of classical LATEX than an XML profile. Most actors in the world of markup have re- 2 Why SGML rather than XML? stricted their use of SGML to XML. For that reason The simple answer is that SGML provides better software that handles SGML beyond the realm of emulation of classical LATEX than XML in that XML XML seems to be falling out of maintenance. If requires markup elements to have tags for both start the LATEX community wishes to continue to be able and end, whereas with SGML it is commonly possible to avail itself of the advantages of SGML for LATEX to omit an end tag and less commonly possible to source emulation, it may fall on the LATEX community omit a start tag and sometimes both. This is not the to maintain the extant SGML libraries. place to rehearse the conditions under which these tag omissions are allowed. The point is that classical LAT X may be viewed as allowing many tag omissions, 1 Maximally useful source markup E and for that reason one may construct approximate Authors spend a great deal of time writing their SGML models that are closer to classical LATEX than articles and reports. Because of that investment any XML model can be. of time it is important that tools used in writing One aspect of the overall idea of generalized are chosen carefully. One wants the fruit of one’s LATEX is that the processing should proceed through writing to be presentable not only on the printed a pipeline with well-defined stages, and the first page but also on screens of various sizes from mobile stage of that processing should involve only syntax. telephones to full-wall monitors. It is better to write Thus, for a particular LATEX markup structure, a once and then use robust processing streams for the human may see how to use code to reformulate it desired output formats rather than to edit manually directly under an XML document type, but that for each output. Within the realm of TEX-like source, formulation might require knowledge of both classical the best results flow from profiled LATEX. LATEX vocabulary and the vocabulary of the XML document type. 1.1 The concept of LATEX Profiles 3 Example: A simple table ALATEX profile is a dialect of LATEX with a fixed command vocabulary, where all macro expansions There follows a mundane example of a centered table A must be effective in that vocabulary, having dual that would normally be created in LTEX using a existence under an SGML [4] document type with tabular environment inside a center environment. a canonical XML [2] shadow. I spoke about this long phrase five shorter concept in my talk [7] on the 1000002-th (i.e., 32nd) shorter long phrase five anniversary of TUG in 2010. While an instance of a LATEX profile may be The pattern of horizontal alignment in the cells of this written directly as SGML or XML using the regular table is “rcr”, which in LATEX is normally furnished syntax, it is envisioned that one would want to use as an argument of the tabular environment. This generalized LATEX, i.e., write using the syntax of table has two rows, each with three cells. The rows LATEX. have horizontal borders and the cells have vertical The XML guise of a LATEX profile can be styled, borders. though with less than perfection, using CSS [1]. See In the GELLMU Didactic Production System my talk [8] at TUG 2014. This is not a new idea this centered table can be marked up with
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\begin{display} with “|”, so long as emulation of TEX’s manmac is \begin{tabular}{|r|c|r|} not being engaged.) \hline At the next stage of processing — under an long phrase & five & shorter \\ SGML transformation — using code with knowledge \hline of markup vocabulary at both ends, the SGML seg- shorter & long phrase & five \\ ment above is transformed to the following XML \hline segment: \end{tabular}
(In this example “
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matter an SGML user must have a collection of aux- for variations of syntax, detailed character set speci- iliary documents just as a LATEX user must have a fication, and myriad markup shortcuts to the point collection of packages. While this can be practical for that I do not know whether any library was ever sharing among a group of authors, it makes sharing produced to provide functions for handling a full an SGML document across the web more difficult implementation of the SGML specification. However, and less efficient than sharing an XML document. the extent of SGML use that I think desirable for SGML documents that are not XML have effec- profiling LATEX is well within the territory covered tively vanished from the web.2 The fact that any new by SGML libraries. SGML documents being generated are behind closed 5.1 Simplicity with XML doors, together with a somewhat steeper learning curve for SGML than for XML, seems to have led to With the rise of XML and the ease of writing software a loss of interest in SGML beyond XML. for parsing and transforming XML documents, many new options appeared. With XML a document need 4.2 Who the authors are not be accompanied by a document type definition. How do SGML and XML documents arise? It is sufficient that transforming software knows the I believe most of the books and articles written markup vocabulary used with the document. Thus: by actual authors, whether for academic publication • An XML document may be rendered in a web or for the popular press, are most likely written either browser solely by linking the document to a CSS with a word processor, such as provided by Microsoft, stylesheet. or in a TEX-family markup. • An XML document may be transformed to an- I believe that most extant SGML or XML doc- other format by using an XSLT transformation uments are not actual source. For example, there that is defined by creating an XSLT stylesheet, are “markdown” languages from which basic XML which itself is an XML document. documents can robustly be spawned. When SGML My guess is that XSLT is probably the most widely or XML documents are actual source, the creators used transformation language for XML today. Per- are usually persons working, one way or another, in sonally, I find it cumbersome to write for XSLT.I document technology. Those creators usually work would much rather code in a traditional programming with editing tools that have been adapted to mini- language. In particular, it is not pleasant trying to mize the distinctions between SGML and XML that code for XSLT when the translation target is LATEX. I mentioned earlier in section 2. I see the LATEX community as still under chal- 5.2 The libraries OpenSP and SGMLSPM lenge by the concern raised by Chris Rowley at the I believe that the most widely deployed library for 2010 TUG meeting over “peak TEX” (analogous to handling SGML is OpenSP. It is a C++ library for “peak oil”), and here I’ve pointed to SGML (beyond parsing and transforming SGML documents that was XML) being in decline. One of the threats for the spawned from James Clark’s SP. Before the rise of future of LATEX is its difficulty in being converted to XML, I believe Clark’s SP was dominant. For exam- other formats for documents where that is sensible. ple, at some point during the time of Sun Microsys- The concept of a LATEX profile provides a place where tems’ Solaris operating system, the system manual LATEX and SGML can help each other to the benefit pages were re-coded from Roff source to a variant of of both. Docbook SGML, and SP was deployed for generating various output formats. This arrangement for sys- 5 Libraries for parsing and processing tem manual pages is found today in Ubuntu systems Because the rules for an XML document are some- though with OpenSP rather than SP. It’s not always what more restrictive than the rules for an SGML understood that since every XML document may be document, libraries for processing XML are easier to construed as an SGML document, OpenSP can be construct and maintain than libraries for processing used with XML documents. SGML. Indeed, the specification of SGML provides I might also mention OpenJade, which was spawned from Jade, also by James Clark. OpenJade 2 There was a time after the rise of XML that version 4 of HTML, an SGML “application” (document type), was provides an engine for Document Style Semantics and the dominant markup for web pages. It worked because web Specification Language (DSSSL), which is an early browsers were required to have native knowledge of HTML. transformation language for SGML that is written This continued for a while even after the early XML form of in SGML — thus, a forerunner of XSLT — under an HTML was promoted and then appeared to gain widespread use through many web page instances that were not actually SGML declaration that makes one of its stylesheets well-formed XML. look like Lisp code. Usually package management
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systems that house OpenSP also house OpenJade; I [3] S. Faulkner, A. Eicholz, et al., HTML 5.2, mention this because online searches for “openjade” World Wide Web Consortium Recommendation, can be easier than for “opensp”. 14 December 2017. Finally, I want to mention the Perl software w3.org/TR/2017/REC-html52-20171214 SGMLSPM/sgmlspl for SGML transformations writ- [4] Charles F. Goldfarb, The SGML Handbook, ten by David Megginson of Ottawa and released as Clarendon Press, Oxford, 1990. GPL software in 1995 that, to my knowledge — I use [5] William F. Hammond, “GELLMU: A Bridge it daily3 — has never since needed repair. SGML- for Authors from LATEX to XML”, TUGboat SPM/sgmlspl enables one to write a handler for each 22:3 (2001), pp. 204–207. element in an SGML (or XML) document type to tug.org/TUGboat/tb22-3/tb72hammond.pdf treat the rendering of that element in a translation. [6] William F. Hammond, “Dual presentation It is designed to accept a parsed stream from OpenSP with math from one source using GELLMU”, and generate an output stream in the target format. TUGboat 28:3 (2007), pp. 306–311. This works well for writing HTML,LAT X, and just E tug.org/TUGboat/tb28-3/tb90hammond.pdf about any output format. If the handlers are not A video of the presentation at TUG 2007, written mindlessly, a single run of OpenSP piped to July 2007, in San Diego is available at SGMLSPM/sgmlspl can handle a very large docu- http://zeeba.tv/conferences/tug-2007. ment. Also there is the advantage that inside one A of those handlers, the transformation writer has the [7] William F. Hammond, “LTEX profiles as full power of Perl. objects in the category of markup languages”, TUGboat 31:2 (2010), pp. 240–247. 5.3 OpenSP needs maintenance tug.org/TUGboat/tb31-2/tb98hammond.pdf. Unfortunately, as it is today, OpenSP only supports A video of the presentation at TUG 2010, the basic multilingual plane of Unicode (U+0000– June 2010, in San Francisco is available at U+FFFF). Tackling the task of adding support for http://zeeba.tv/conferences/tug-2010. all of Unicode might not at first glance seem hard, but [8] William F. Hammond, “Can LATEX profiles it is daunting because of the complexity of OpenSP be rendered adequately with static CSS?”, that arises from the extent of its coverage of SGML TUGboat 35:2 (2014), pp. 212–218. beyond XML and its character handling. To my mind tug.org/TUGboat/tb35-2/tb110hammond.pdf this task might be a good master’s thesis project for A video recording of the presentation at someone in Computer Science. Prior to modification TUG 2014, June 2014, in Portland, Oregon is the code will require much study. The task needs available at http://zeeba.tv/conferences/ someone with stamina and good eyes. text/tex/tug-2014. [9] Leslie Lamport, LATEX: A Document References Preparation System, 2nd edition, [1] Bert Bos, Tantek C¸ elik, Ian Hickson, & H˚akon Addison-Wesley, 1994. Wium Lie, Cascading Style Sheets Level 2 [10] MacFarlane, John, Pandoc: A Universal Revision 1 (CSS 2.1) Specification, World Document Converter. Wide Web Consortium Recommendation, 7 pandoc.org June 2011. w3.org/TR/2011/REC-CSS2-20110607 William F. Hammond [2] Tim Bray, Jean Paoli, C.M. Sperberg-McQueen, University at Albany, Eve Maler, & Fran¸cois Yergeau, Extensible Albany, New York, and Markup Language (XML) 1.0 (Fifth San Diego, California Edition), World Wide Web Consortium whammond (at) albany dot edu Recommendation, 26 November 2008. https://www.albany.edu/ w3.org/TR/2008/REC-xml-20081126 ~hammond/
3 After incorporating one additional feature written by Dave Walden.
William F. Hammond