W. F. Hammond: The GELLMU ArchiveWilliam F. Hammond

Department of Mathematics Statistics The University at Albany Albany, NY 12222, USA

September 2000 Last revision: (still needs revision as well as a better proof reading)Note: Since this document was written, there have been some enhancements to the system it describes For more information see the href="http:www.albany.eduhammondgellmuglmanglman.html"GELLMU Manual

Another MarkUp Language?The purpose of regular GELLMUGELLMU stands for Generalized Extensible like MarkUp is to provide a markup language with provision for mathematics under a system design that is structured enough to admit rigorous, modularlystaged, automatic processing into many other formats while at the same time being a comfortable input format for those accustomed to using There is not a set list of translation target formats Examples of possible translation targets include: HTMLHTML as enhanced by MathMLTexinfoME (a roff package)textplain (for optimal deing)audio streamsearch engineindex engineGELLMU is not although its style of markup resembles that of An example of how there is provision for enrichment of information lies in the markup used for a quoted phrase in the href="http:www.albany.eduhammondgellmuigliglm.glm"source for this document.The base for relative URI references given here may be found at the end of the printed form of this document. Whereas the usual way of writing the phrase in the last sentence would be enrichment of information, and that markup would be meaningful in regular GELLMU, the markup quophraseenrichment of information can be detected more easily by a processor looking for quophrase contents, while the separate doublequoting indicators may or may not be adequate for such a processor seeking to glean similar information Furthermore, the effort by a processor to glean such information might be spoiled by the occurrence of one or more unbalanced doublequoting indicators Possibly even more useful ways of marking the same phrase that still would yield the same printed appearance, depending on the overall context, might be: jargonenrichment of information or topicenrichment of information.An important characteristic of this markup is that the processing of a document always begins with a faithful translation to an instance under the umbrella of Standard Generalized Markup Language (SGML) It is widely known in the text processing community (though not widely observed in the mathematical community) that sufficiently structured markup languages under SGML can be robustly converted to many other formats GELLMU has been designed to provide a bridge from LaTeXlike markup to the world of SGMLThe translation from source markup to SGML markup is performed by my program called the GELLMU Syntactic Translator Once that translation is performed the authors document exists in the world of SGML, and in that world many programs, almost all of which are very highly configurable, are available for automatic processingBeyond the syntactic translation from source markup to SGML the first release of materials from this project will contain a didactic article SGML document type, and some of the statements herein are, for illustration, nonexplicit allusions to the article document type, which is just one example of an SGML document type in the advanced GELLMU categoryRealistically today, SGML is a document standard for inhouse work, and its subset XMLSubcategory might be a better term here than subset. has become the only shareable form of SGML Major SGML document types such as DocBook and TEI have canonical translations to XML Still one does not abandon SGML in an authoring environment, because some of the features of full SGML provide substantial convenience for authorsWhat added convenience there is in using like markup as a writing interface for XML is greatly aided by taking advantage of a few of the features in full SGML that are not available in XML On the other hand, basic GELLMU is available for the direct preparation of an XML document as the direct output of the syntactic translator

How did GELLMU arise?Aside from markup languages under SGML another example of a markup language that is structured enough to admit robust conversion is Texinfo, which is the markup language of The href="http:www.gnu.org"GNU Documentation System The Info side of Texinfo is the Info hypertext selfdocumentation system within the popular fully programmable editing system GNU Emacs Documents authored in Texinfo can be automatically converted into both Info (for viewing in an GNU Emacs buffer) and (for printing)The Info system is a hypertext system that predates the World Wide Web (WWW) and the latters default presentation markup language known as HTML, which falls under the SGML regime One should, therefore, not be surprised to learn that with the dawn of HTML Lionel Cons of CERN (the birthplace of the World Wide Web) furnished the world with a PERL program for converting a Texinfo document into HTML with (internal) hypertext referencesAlthough Texinfo is a like markup language, it makes wide use of the character as commandintroducer where in one would (normally) use It seems that many authors find this superficial difference uncomfortable Ulrik Vieth of href="http:www.tug.org"The Users Group (TUG) wrote an Emacs Lisp program that served to convert into Texinfo a file written in January 1998 as the href "ftp:ctan.tug.orgtexarchivetdsdraftstandardtds0.9995.tar.gz"draft report of the TUG Working Group on a directory structure for systemsThis example, which was an ad hoc conversion, played an important role in my arrival at this design for a bridge from to SGML

Translation of GELLMU MarkupGELLMU is essentially, but for appearance, a markup language under SGML This means that after a document is translated by the syntactic translator into the corresponding markup language falling formally under SGML, any generalpurpose SGML processing tool can be usedThe projects prototype production system is built around Regular GELLMU, which uses features for enhanced authoring convenience in the syntactic translator that require some assumptions about the SGML document type under which the author is writing Basic GELLMU, on the other hand, may be used as a simple like markup interface with a large number of document types, including XML document typesTwo SGML processing tools that are easily available form the core of the prototype production system James Clarks nsgmls, an SGML parser that is part of his href="ftp:ftp.jclark.compubsp"SP library package David Megginsons PERL program sgmlspl that is an interface for his Perl library SGMLSPM. It may be found at href="http:www.cpan.orgmodulesbyauthorsDavidMegginson"CPAN or at his href="http:www.megginson.com"office sgmlspl is a programmerfriendly interface for writing simple or complex eventdriven translators (to other formats) that operate on nsgmls output In the prototype production system a document under the didactic article SGML document type made with the GELLMU Syntactic Translator from like source markup is parsed by nsgmls and then passed through a simple sgmlspl translation to yield an instance under the corresponding XML document typeIn the prototype production system the XML version of an article may be translated either to HTML or to Other translations are possible The two existing translations are done with sgmlsplBut a number of other freely available translation tools may be considered for the XML version of a GELLMU article including: James Clarks jade, an engine for DSSSL with a wide variety of possible translation targets James Clarks xt, an XSLT engine also with a wide variety of possible translation targets David Carlisles xmltex, a package for TeX, the Program, that enables its user to write what amounts to a style sheet in , rather than, say, XSL, for formatting (with its own parse) an instance of an XML document type in (actually DVI since one does not get a chance to see a source image)

Advanced GELLMU vs. Basic GELLMUThis document is about the regular GELLMU It is important first to know a bit about basic mode and advanced mode What is called regular in this document is an instance of advanced mode The term regular is being used here to reference the didactic article document type, which is an SGML document type that admits the more elaborate and succinct handling of advanced mode while not being in any way incompatible with basic modeNeither the basic nor the advanced mode involves in any way adoption of the language of (But many command names under the didactic document type, mimic command names.)To use either basic or advanced mode one must be familiar with the SGML document type for which one is writing Ordinary HTML is an example where the use of basic mode is indicated Only a very few of the features in advanced markup not part of basic markupWith several minor exceptions, one related to the direct writing of SGML attributes (which cannot contain markup and which do not have many parallels in ) and another related to the way of escaping the character , everything about basic mode also applies to advanced mode. make any sense for use in the direct preparation of HTML with like inputBasic GELLMU uses the special characters , , and along with like argumentoption syntax, where braces immediately following a command name indicate command arguments and square brackets, i.e., and , 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 a[href="http:www.w3.org"]The World Wide Web Consortium to form the HTML anchor: a href="http:www.w3.org"The World Wide Web Consortiuma (The formation of anchors with the didactic document type in advanced mode is slightly more complicated because the characters and , 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 argumentoption syntax, 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 , represent the beginning of a paragraph In basic mode for classical HTML one mustThere is a way, with the setting of several variables for the syntactic translator, to have blank lines begin new paragraphs in basic input for HTML use p 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 waysFor some of the details on using the basic markup with HTML see href="http:www.albany.eduhammondgellmughtml.html"Using the GELLMU Syntactic Translator to Write HTML

Some Fundamentals on Regular GELLMUThe Markup CommandsThere are several kinds of commands:A maximal string introduced by followed by a letterFor the first alpha release letter means something matching the regular expression [AZaz] This will not be a limitation of the syntactic translator after the alpha releases I believe that GNU Emacs, from version 20, is fully capable of meeting the needs of GELLMU for supporting international character sets At present, it is possible to use Emacs word constituent characters in names defined with newcommand, and there is no reason why the definition strings cannot involve standard SGML entity notation It is also possible to define symbolic SGML entities in the SGML internal declaration subset, which is the content of an option (at most one) that follows the unique argument to the metacommand documenttype Additionally, the SGML version of the didactic article document type provides commands for the document preamble that may be used to construct an internal declaration subset for the XML version of the document (Of course, someone using this markup to edit directly for a document type under XML would need to use the documenttype option provided for the SGML internal declaration subset.) and otherwise consisting only of letters and numbers. The first number, if any, must not be 0 since such names are reserved for use by the syntactic translator. Command names are case sensitive Such a command is a container, corresponding to an SGML element, if it is immediately followed, without intervening white space, by the character In that case the delimited zone of containment normally ends with the subsequent balancing character (like multiple argumentoption chains deserve more discussion; for now it will suffice to point out that the use of the anch command in this document for making anchors is an example, and, of course, s frac command is another example For the present discussion these commands are considered to be containers.) Such a command corresponds to an SGML definedempty element if it is followed immediately without intervening white space by the character ; In any other case there is syntactical ambiguity However, the syntactic translator will produce a corresponding SGML open tag unless the logical variable gellmuxmlstrict has been set (This variable is normally not set for advanced GELLMU.) Certain single characters. , , , , , , , and have command meanings that are similar to their meanings in The characters ; and : are ordinary characters that have special meaning at the end of a command name The character is also a special character used, as with , in newcommand templates In source for the didactic article document type any nonalphanumeric ASCII character may be escaped (referenced for itself) with a named command, e.g. may be referenced for itself as pct; 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 regular markup: "": Command introducer Escape in basic mode: "". This escape is incorrect in regular mode For the didactic article document type the escape is "bsl;" For other document types one may resort to an entity reference if there is an aversion to the provision of a corresponding definedempty element or if one lacks control of the document type "": Command argument opener Escape: "" "": Command argument closer Escape: "" "[": Command option opener "]": Command option closer ";": Command terminator for commands corresponding to definedempty SGML elements; otherwise 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 ; as an entity reference terminator in HTML ":": Special purpose command terminator used for indicating the close of a commandzone; otherwise an ordinary character Its use as a command terminator is invisible "": Comment introducer (in force to end of line) Any command is terminated by a nonalphanumeric character There is syntactic ambiguity unless the terminator is one of , , ;, or : This kind of syntactic ambiguity is not permitted in the direct editing for an XML document type with GELLMU input The terminator can be a blank space, but, if so, the blank space becomes invisibleThe following language meanings apply to regular markup with allusion to the didactic article document type "": Nonbreaking interword space Equivalent: nbs;, cf. nbsp; in HTML "": Superscript command Equivalent: sup "": Subscript command Equivalent: sub "": Dual use: tabular cells and entity introducer introduces an entity reference if it is followed by anything other than white space It is used, as in , as a tabular cell delineator when it is followed by white space "": Toggle inline math mode. Equivalent: "tmath . . . " Nearly equivalent: "( . . . )" or "math . . . ".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 .) The syntactic translator resists the temptation here to go beyond syntax, and with the didactic article document type the formatting to inserts the markup , for a small horizontal space before and after math, but not before and after tmath. Certain strings of plain text in regular GELLMU that are part of legacy practice under . "" A short dash as used with a range of numbers, e.g., 12 Equivalent: rdash "" A long dash as used for punctuation, e.g., a dash like this Equivalent: pdash " " Blank interword space Equivalent: spc; "," Small horizontal space Equivalent: hsp; "" A forced line break 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 ) it begins a new tabular row Any other use is deprecated, and will result in translation to the definedempty element bsl corresponding to the ASCII character with a warning from the syntactic translator. The use of tabular is deprecated and is not supported beyond lrc Use table, which is not similar to s table, instead of tabular Equivalents: brk; for a line break outside of a tabular environment.The syntactic translator simply outputs the SGML definedempty 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 nontabular use of brk0 is converted to brk. A blank line. Begin new paragraph command Equivalent: parb Nearly equivalent: par "" Left (double) quotation mark Equivalent: ldq "" Right (double) quotation mark Equivalent: rdq "(" Begin math mode command Equivalent: beginmath ")" End math mode command Equivalent: endmath "[" Begin displaymath mode command Equivalent: begindisplaymath "]" End displaymath mode command Equivalent: enddisplaymath beginname . . . endname This usage is equivalent to name . . . name:, which, in turn, is equivalent to name ... Multiple ArgumentOption SyntaxAn essential point in the present design is that the whole system is built from components, each of which has its own functionIn 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 , enhancement is an ongoing process Consistent with this design the syntactic translator operates with knowledge of syntax but little or no knowledge of languageMultiple argumentoption syntax has been built into advanced mode as part of the overall idea of providing, where sensible, like features in a precise user markup interface for writing in document types under SGML and XMLWhat are the rules for converting the multiple argumentoption 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 One obtains an XML version of a document in the prototype 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 translatorIn multiple argumentoption syntax, which is much like that of , arguments and options follow command names Arguments are delimited by braces, i.e., and and options by square brackets, i.e., and There must be no white space between the arguments and options nor between the command name and the first member of an argumentoption sequenceEach command with a multiple argumentoption 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 lying in GELLMUs reserved name space There are two exceptional cases The first argument or option is an option inside which the very first character is a colon, i.e., : This is the method provided in advanced mode for the direct entry of an SGML attribute sequence The entire contents of the option string, apart from the leading :, 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 semicolon, i.e., the character ;, if and only if the corresponding SGML element is a definedempty element under the SGML document type Since SGML attributes correspond to very little of classical , attribute options may be entirely ignored 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 argumentoption handling since the sole argument simply becomes element content without an ag0 wrapper MathematicsThe Greek letter is marked, up as in , with GammaThe didactic article document type provides mathematical markup that is similar to that of For example, one may use the markup [ 2p1 equiv 1 pmodp2 eos] to speak of the congruence 2^p1 1 p² In this example the markup eos is a formal endofsentenceRegular GELLMU recognizes . followed by two blank spaces or by a newline as endsofsentence markup when these occur outside of mathematical contexts.In a math environment, input text abc is set the same as the the input text a b c following the presumption that each glyph is a separate symbol At one point I had planned to provide for a distinction between these two forms of input for article However, I am concerned about author confusion; so there will be provision for having abc be a math symbol, but an instance will be invoked as abcIn math mode all symbols are assumed to be singlecharacters as in A mathsym command (part of language design that, for the moment, has no extant implementation) in the document preamble may be used to specify that a string is to be regarded as a single mathematical entity whenever it occurs in math mode This contrasts with in that there is no formal declaration of math symbolsmathsym will be a variant of newcommand, which is a metacommand that is handled entirely by the syntactic translator with no trace in the output However, the design of mathsym, which will also be a metacommand but which will leave marks in the output, is not yet decided The design issues surround how to provide the author who is its user with fexible open means of planting semantic information in the output without undue verbosity The syntax might be simply mathsymsymbolname presentationdefintion semanticinformationwithoutmarkup Omitting the option could make author usage equivalent to that of newcommand, but still trace information planted in the output of the syntactic translator could be sufficient that in the future a derived MathML object or a derived XML formatted object produced by translation and viewed in href="http:www.mozilla.org"Mozilla might enable the reader to ascertain the symbolname and then launch a search for other occurrences The option would serve as a mechanism for the author to pass semantic enrichment information to downstream formatters ExamplesThe following table refers to the didatic article document type It demonstrates how source is translated by the GELLMU Syntactic Translator to the SGML version of article and from there is translated using sgmlspl to the XML version of article ll

Source	emphthis
SGML	emphthisemph
XML	emphthisemph
Source	tex;
SGML	tex
XML	tex
Source	frac23
SGML	tmath fracag02ag0ag03ag0 tmath
XML	tmath fracnumr2numrdenm3denmfractmath
Source	anch[href="nil"]Nullanch:
SGML	anchop0hrefeqs"nil"op0ag0Nullag0anch
XML	anchanchrefhref="nil"anchrefanchvNullanchvanch

One may find many other examples of GELLMU markup in the href="http:www.albany.eduhammondgellmu"project archive

NotesAlthough the metacommand newcommand, which is handled internally by the syntactic translator, is now available, the variant metacommand mathsym is not yet availableThis document is still at draft stageIt is itself a GELLMU document The following versions are available: href="http:www.albany.eduhammondgellmuigliglm.glm"sourcehref="http:www.albany.eduhammondgellmuigliglm.sgml"SGMLhref="http:www.albany.eduhammondgellmuigliglm.xml"XMLhref="http:www.albany.eduhammondgellmuigliglm.xhtml"XHTML with MathMLhref="http:www.albany.eduhammondgellmuigliglm.html"classic HTMLhref="http:www.albany.eduhammondgellmuigliglm.ltx"href="http:www.albany.eduhammondgellmuigliglm.dvi"DVI