SGML-Tools User's Guide by Matt Welsh. Updated by Greg Hankins, rewritten by Eric S. Raymond. 1.0 ($Revision: 1.7 $), 10 November 1997 This document is a user's guide to the SGML-Tools formatting system, a SGML-based system which allows you to produce a variety of output for- mats. You can create plain text output (ASCII and ISO-8859-1), DVI, PostScript, HTML, GNU info, LyX, and RTF output from a single document source file. This guide describes SGML-Tools version 1.0. ______________________________________________________________________ Table of Contents 1. Introduction 2. Installation 2.1 What SGML-Tools Needs 2.2 Installing The Software 3. Writing Documents With SGML-Tools 3.1 Basic Concepts 3.2 Special Characters 3.3 Verbatim and Code Environments 3.4 Overall Document Structure 3.4.1 The Preamble 3.4.2 Sectioning And Paragraphs 3.4.3 Ending The Document 3.5 Internal Cross-References 3.6 Web References 3.7 Fonts 3.8 Lists 3.9 Conditionalization 3.10 Index generation 3.11 Controlling justification 4. Formatting SGML Documents 4.1 Checking SGML Syntax 4.2 Creating Plain Text Output 4.3 Creating LaTeX, DVI or PostScript Output 4.4 Creating HTML Output 4.5 Creating GNU Info Output 4.6 Creating LyX Output 4.7 Creating RTF Output 5. Internationalization Support 6. How SGML-Tools Works 6.1 Overview of SGML 6.2 How SGML Works 6.3 What Happens When SGML-Tools Processes A Document 6.4 Further Information ______________________________________________________________________ 11.. IInnttrroodduuccttiioonn SGML-Tools is a suite of programs to help you write source documents that can be rendered as plain text, hypertext, or high-quality typeset markup suitable for printing books. This document is the user's guide to the SGML-Tools document processing system. It contains more or less everything you need to know to set up SGML-Tools and write documents using it. See example.sgml for an example of an SGML document that you can use as a model for your own documents. 22.. IInnssttaallllaattiioonn You can get sgml-tools-1.0.x.tar.gz from: +o http://pobox.com/~cg/sgmltools 22..11.. WWhhaatt SSGGMMLL--TToooollss NNeeeeddss The file sgml-tools-1.0.x.tar.gz contains everything that you need to write SGML documents and convert them to groff, LaTeX, PostScript, HTML, GNU info, LyX, and RTF. In addition to this package, you will need some additional tools for generating formatted output. 1. groff. You _n_e_e_d version 1.08 or greater. You can get this from ftp://prep.ai.mit.edu/pub/gnu. There is a Linux binary version at ftp://sunsite.unc.edu/pub/Linux/utils/text as well. You will need groff to produce plain text from your SGML documents. nroff will _n_o_t work! You can find the version of your groff from groff -v < /dev/null. 2. TeX and LaTeX. This is available more or less everywhere; you should have no problem getting it and installing it (there is a Linux binary distribution on sunsite.unc.edu). Of course, you only need TeX/LaTeX if you want to format your SGML documents with LaTeX. So, installing TeX/LaTeX is optional. 3. flex. lex will probably not work. You can get flex from ftp://prep.ai.mit.edu/pub/gnu. 4. gawk and the GNU info tools, for formatting and viewing info files. These are also available on ftp://prep.ai.mit.edu/pub/gnu, or on ftp://sunsite.unc.edu/pub/Linux/utils/text (for gawk) and ftp://sunsite.unc.edu/pub/Linux/system/Manual-pagers (for GNU info tools). awk will not work. 5. LyX (a quasi-WYSIWYG interface to LaTeX, with SGML layouts), is available on ftp://ftp.via.ecp.fr. 22..22.. IInnssttaalllliinngg TThhee SSooffttwwaarree The steps needed to install and configure the SGML-Tools are: 1. First, unpack the tar file sgml-tools-1.0.x.tar.gz somewhere. This will create the directory sgml-tools-1.0.x. It doesn't matter where you unpack this file; just don't move things around within the sgml-tools-1.0.x directory. 2. Read the INSTALL file - it has detailed installation instructions. Follow them. If all went well, you should be ready to use the system immediately once you have done so. 33.. WWrriittiinngg DDooccuummeennttss WWiitthh SSGGMMLL--TToooollss For the most part, writing documents using SGML-Tools is very simple, and rather like writing HTML. However, there are some caveats to watch out for. In this section we'll give an introduction on writing SGML documents. See the file example.sgml for a SGML example document (and tutorial) which you can use as a model when writing your own documents. Here we're just going to discuss the various features of SGML-Tools, but the source is not very readable as an example. Instead, print out the source (as well as the formatted output) for example.sgml so you have a real live case to refer to. 33..11.. BBaassiicc CCoonncceeppttss Looking at the source of the example document, you'll notice right off that there are a number of ``tags'' marked within angle brackets (< and >). A tag simply specifies the beginning or end of an element, where an element is something like a section, a paragraph, a phrase of italicized text, an item in a list, and so on. Using a tag is like using an HTML tag, or a LaTeX command such as \item or \section{...}. As a simple example, to produce tthhiiss bboollddffaacceedd tteexxtt, you would type As a simple example, to produce this boldfaced text, ... in the source. begins the region of bold text, and ends it. Alternately, you can use the abbreviated form As a simple example, to produce tag, however, the end- tag for the section (which could appear at the end of the section body itself, not just after the name of the section!) is optional and implied when you start another section of the same depth. In general you needn't worry about these details; just follow the model used in the tutorial (example.sgml). 33..22.. SSppeecciiaall CChhaarraacctteerrss Obviously, the angle brackets are themselves special characters in the SGML source. There are others to watch out for. For example, let's say that you wanted to type an expression with angle brackets around it, as so: . In order to get the left angle bracket, you must use the < element, which is a ``macro'' that expands to the actual left-bracket character. Therefore, in the source, I typed angle brackets around it, as so: <foo>. Generally, anything beginning with an ampersand is a special charac- ter. For example, there's % to produce %, | to produce |, and so on. For every special character that might otherwise con- fuse SGML-Tools if typed by itself, there is an ampersand "entity" to represent it. The most commonly used are: +o Use & for the ampersand (&), +o Use < for a left bracket (<), +o Use > for a right bracket (>), +o Use &etago; for a left bracket with a slash (>)) greater-than sign &&ddiivviiddee ((//)) division sign &&ttiimmeess ((xx)) multiplication sign &&ccuurrrreenn (({{ccuurrrreenn}})) currency symbol &&ppoouunndd ((LL)) symbol for ``pounds'' &&ddoollllaarr (($$)) dollar sign &&cceenntt ((cc)) cent sign &&yyeenn ((YY)) yen sign &&nnuumm ((##)) number or hash sign &&ppeerrccnntt ((%%)) percent sign &&aammpp ((&&)) ampersand &&aasstt ((**)) asterisk &&ccoommmmaatt ((@@)) commercial-at sign &&llssqqbb (([[)) left square bracket &&bbssooll ((\\)) backslash &&rrssqqbb ((]])) right square bracket &&llccuubb (({{)) left curly brace &&hhoorrbbaarr ((--)) horizontal bar &&vveerrbbaarr ((||)) vertical bar &&rrccuubb ((}})) right curly brace &&mmiiccrroo ((uu)) greek mu (micro prefix) &&oohhmm (({{oohhmm}})) greek capital omega (Ohm sign) &&ddeegg (({{ddeegg}})) small superscript circle sign (degree sign) &&oorrddmm (({{oorrddmm}})) masculine ordinal &&oorrddff (({{oorrddff}})) feminine ordinal &&sseecctt ((SS)) section sign &&ppaarraa ((PP)) paragraph sign &&mmiiddddoott ((..)) centered dot &&llaarrrr ((<<--)) left arrow &&rraarrrr ((-->>)) right arrow &&uuaarrrr (({{uuaarrrr}})) up arrow &&ddaarrrr (({{ddaarrrr}})) down arrow &&ccooppyy ((((CC)))) copyright &&rreegg ((((RR)))) r-in-circle marl &&ttrraaddee ((((TTMM)))) trademark sign &&bbrrvvbbaarr ((||)) broken vertical bar &&nnoott ((~~)) logical-negation sign &&ssuunngg (({{ssuunngg}})) sung-note sign &&eexxccll ((!!)) exclamation point &&iieexxccll ((!!)) inverted exclamation point &&qquuoott (("")) double quote &&aappooss (('')) apostrophe (single quote) &&llppaarr (((()) left parenthesis &&rrppaarr (()))) right parenthesis &&ccoommmmaa ((,,)) comma &&lloowwbbaarr ((__)) under-bar &&hhyypphheenn ((--)) hyphen &&ppeerriioodd ((..)) period &&ssooll ((//)) solidus &&ccoolloonn ((::)) colon &&sseemmii ((;;)) semicolon &&qquueesstt ((??)) question mark &&iiqquueesstt ((??)) interrobang &&llaaqquuoo ((<<<<)) left guillemot &&rraaqquuoo ((>>>>)) right guillemot &&llssqquuoo ((``)) left single quote &&rrssqquuoo (('')) right single quote &&llddqquuoo ((````)) left double quote &&rrddqquuoo (('''')) right double quote &&nnbbsspp (( )) non-breaking space &&sshhyy (()) soft hyphen 33..33.. VVeerrbbaattiimm aanndd CCooddee EEnnvviirroonnmmeennttss While we're on the subject of special characters, we might as well mention the verbatim ``environment'' used for including literal text in the output (with spaces and indentation preserved, and so on). The verb element is used for this; it looks like the following: Some literal text to include as example output. The verb environment doesn't allow you to use _e_v_e_r_y_t_h_i_n_g within it literally. Specifically, you must do the following within verb envi- ronments. +o Use &ero; to get an ampersand, +o Use &etago; to get Here is some example text. tscreen is an environment that simply indents the text and sets the sets the default font to tt. This makes examples look much nicer, both in the LaTeX and plain text versions. You can use tscreen with- out verb, however, if you use any special characters in your example you'll need to use both of them. tscreen does nothing to special characters. See example.sgml for examples. The quote environment is like tscreen, except that it does not set the default font to tt. So, you can use quote for non-computer- interaction quotes, as in: Here is some text to be indented, as in a quote. which will generate: Here is some text to be indented, as in a quote. 33..44.. OOvveerraallll DDooccuummeenntt SSttrruuccttuurree Before we get too in-depth with details, we're going to describe the overall structure of an SGML-tools document. Look at example.sgml for a good example of how a document is set up. 33..44..11.. TThhee PPrreeaammbbllee In the document ``preamble'' you set up things such as the title information and document style:
Linux Foo HOWTO <author>Norbert Ebersol, <tt/norb@baz.com/ <date>v1.0, 9 March 1994 <abstract> This document describes how to use the <tt/foo/ tools to frobnicate bar libraries, using the <tt/xyzzy/ relinker. </abstract> <toc> The elements should go more or less in this order. The first line tells the SGML parser to use the linuxdoc DTD. We'll explain that in the later section on ``How SGML-Tools Works''; for now just treat it as a bit of necessary magic. The <article> tag forces the document to use the ``article'' document style. The title, author, and date tags should be obvious; in the date tag include the version number and last modification time of the document. The abstract tag sets up the text to be printed at the top of the document, _b_e_f_o_r_e the table of contents. If you're not going to include a table of contents (the toc tag), you probably don't need an abstract. 33..44..22.. SSeeccttiioonniinngg AAnndd PPaarraaggrraapphhss After the preamble, you're ready to dive into the document. The following sectioning commands are available: +o sect: For top-level sections (i.e. 1, 2, and so on.) +o sect1: For second-level subsections (i.e. 1.1, 1.2, and so on.) +o sect2: For third-level subsubsections. +o sect3: For fourth-level subsubsubsections. +o sect4: For fifth-level subsubsubsubsections. These are roughly equivalent to their LaTeX counterparts section, subsection, and so on. After the sect (or sect1, sect2, etc.) tag comes the name of the section. For example, at the top of this document, after the preamble, comes the tag: <sect>Introduction And at the beginning of this section (Sectioning and paragraphs), there is the tag: <sect2>Sectioning And Paragraphs After the section tag, you begin the body of the section. However, you must start the body with a <p> tag, as so: <sect>Introduction <p> This is a user's guide to the SGML-Tools document processing... This is to tell the parser that you're done with the section title and are ready to begin the body. Thereafter, new paragraphs are started with a blank line (just as you would do in TeX). For example, Here is the end of the first paragraph. And we start a new paragraph here. There is no reason to use <p> tags at the beginning of every para- graph; only at the beginning of the first paragraph after a sectioning command. 33..44..33.. EEnnddiinngg TThhee DDooccuummeenntt At the end of the document, you must use the tag: </article> to tell the parser that you're done with the article element (which embodies the entire document). 33..55.. IInntteerrnnaall CCrroossss--RReeffeerreenncceess Now we're going to move onto other features of the system. Cross- references are easy. For example, if you want to make a cross- reference to a certain section, you need to label that section as so: <sect1>Introduction<label id="sec-intro"> You can then refer to that section somewhere in the text using the expression: See section <ref id="sec-intro" name="Introduction"> for an introduction. This will replace the ref tag with the section number labeled as sec- intro. The name argument to ref is necessary for groff and HTML translations. The groff macro set used by SGML-Tools does not cur- rently support cross-references, and it's often nice to refer to a section by name instead of number. For example, this section is ``Cross-References''. Some back-ends may get upset about special characters in reference labels. In particular, latex2e chokes on underscores (though the latex back end used in older versions of this package didn't). Hyphens are safe. 33..66.. WWeebb RReeffeerreenncceess There is also a url element for Universal Resource Locators, or URLs, used on the World Wide Web. This element should be used to refer to other documents, files available for FTP, and so forth. For example, You can get the Linux HOWTO documents from <url url="http://sunsite.unc.edu/mdw/HOWTO/" name="The Linux HOWTO INDEX">. The url argument specifies the actual URL itself. A link to the URL in question will be automatically added to the HTML document. The optional name argument specifies the text that should be anchored to the URL (for HTML conversion) or named as the description of the URL (for LaTeX and groff). If no name argument is given, the URL itself will be used. For example, you can get the SGML-Tools package from ftp://sunsite.unc.edu/pub/Linux/utils/text/sgml-tools-1.0.x.tar.gz. A useful variant of this is htmlurl, which suppresses rendering of the URL part in every context except HTML. What this is useful for is things like a person's email addresses; you can write <htmlurl url="mailto:esr@snark.thyrsus.com" name="esr@snark.thyrsus.com"> and get ``esr@snark.thyrsus.com'' in text output rather than the duplicative ``esr@snark.thyrsus.com <mailto:esr@snark.thyrsus.com>'' but still have a proper URL in HTML documents. 33..77.. FFoonnttss Essentially, the same fonts supported by LaTeX are supported by SGML- Tools. Note, however, that the conversion to plain text (through groff) does away with the font information. So, you should use fonts as for the benefit of the conversion to LaTeX, but don't depend on the fonts to get a point across in the plain text version. In particular, the tt tag described above can be used to get constant- width ``typewriter'' font which should be used for all e-mail addresses, machine names, filenames, and so on. Example: Here is some <tt>typewriter text</tt> to be included in the document. Equivalently: Here is some <tt/typewriter text/ to be included in the document. Remember that you can only use this abbreviated form if the enclosed text doesn't contain slashes. Other fonts can be achieved with bf for bboollddffaaccee and em for _i_t_a_l_i_c_s. Several other fonts are supported as well, but we don't suggest you use them, because we'll be converting these documents to other formats such as HTML which may not support them. Boldface, typewriter, and italics should be all that you need. 33..88.. LLiissttss There are various kinds of supported lists. They are: +o itemize for bulleted lists such as this one. +o enum for numbered lists. +o descrip for ``descriptive'' lists. Each item in an itemize or enum list must be marked with an item tag. Items in a descrip are marked with tag. For example, <itemize> <item>Here is an item. <item>Here is a second item. </itemize> Looks like this: +o Here is an item. +o Here is a second item. Or, for an enum, <enum> <item>Here is the first item. <item>Here is the second item. </enum> You get the idea. Lists can be nested as well; see the example docu- ment for details. A descrip list is slightly different, and slightly ugly, but you might want to use it for some situations: <descrip> <tag/Gnats./ Annoying little bugs that fly into your cooling fan. <tag/Gnus./ Annoying little bugs that run on your CPU. </descrip> ends up looking like: GGnnaattss.. Annoying little bugs that fly into your cooling fan. GGnnuuss.. Annoying little bugs that run on your CPU. 33..99.. CCoonnddiittiioonnaalliizzaattiioonn The overall goal of SGML-tools is to be able to produce from one set of masters output that is semantically equivalent on all back ends. Nevertheless, it is sometimes useful to be able to produce a document in slightly different variants depending on back end and version. SGML-tools supports this through the <#if> and <#unless> bracketing tags. These tags allow you to selectively include and uninclude portions of an SGML master in your output, depending on filter options set by your driver. Each tag may include a set of attribute/value pairs. The most common are ``output'' and ``version'' (though you are not restricted to these) so a typical example might look like this: Some <#if output=latex version=drlinux>conditional</#if> text. Everything from this <#if> tag to the following </#if> would be con- sidered conditional, and would not be included in the document if either the filter option ``output'' were set to something that doesn't match ``latex'' or the filter option ``version'' were set to something that doesn't match ``drlinux''. The double negative is deliberate; if no ``output'' or ``version'' filter options are set, the conditional text will be included. Filter options are set in one of two ways. Your format driver sets the ``output'' option to the name of the back end it uses; thus, in particular, sgml2latex sets ``output=latex2e'', Or you may set an attribute-value pair with the -D option of your format driver. Thus, if the above tag were part of a file a file named ``foo.sgml'', then formatting with either % sgml2latex -Dversion-drlinux foo.sgml or % sgml2latex foo.sgml would include the ``conditional'' part, but neither % sgml2html -Dversion-drlinux foo.sgml nor % sgml2latex -Dprivate-book foo.sgml would do so. So that you can have conditionals depending on one or more of several values matching, values support a simple alternation syntax using ``|''. Thus you could write: Some <#if output="latex|html" version=drlinux>conditional</#if> text. and formatting with either sgml2latex or sgml2html will include the ``conditional'' text (but formatting with, say, sgml2txt will not). The <#unless> tag is the exact inverse of <#if>; it includes when <#if>; would exclude, and vice-versa. Note that these tags are implemented by a preprocessor which runs before the SGML parser ever sees the document. Thus they are completely independent of the document structure, are not in the DTD, and usage errors won't be caught by the parser. You can seriously confuse yourself by conditionalizing sections that contain unbalanced bracketing tags. The preprocessor implementation also means that standalone SGML parsers will choke on SGML-tools documents that contain conditionals. However, you can validity-check them with the sgmlcheck tool. Also note that in order not to mess up the source line numbers in parser error messages, the preprocessor doesn't actually throw away everything when it omits a conditionalized section. It still passes through any newlines. This leads to behavior that may suprise you if you use <if> or <unless> within a <verb> environment, or any other kind of bracket that changes SGML's normal processing of whitespace. These tags are called ``#if'' and ``#unless'' (rather than ``if'' and ``unless'') to remind you that they are implemented by a preprocessor and you need to be a bit careful about how you use them. 33..1100.. IInnddeexx ggeenneerraattiioonn To support automated generation of indexes for book publication of SGML masters, SGML-tools supports the <idx> and <cdx> tags. These are bracketing tags which cause the text between them to be saved as an index entry, pointing to the page number on which it occurs in the formatted document. They are ignored by all backends except LaTeX, which uses them to build a .ind file suitable for processing by the TeX utility makeindex. The two tags behave identically, except that <idx> sets the entry in a normal font and <cdx> in a constant-width one. If you want to add an index entry that shouldn't appear in the text itself, use the <nidx> and <ncdx> tags. 33..1111.. CCoonnttrroolllliinngg jjuussttiiffiiccaattiioonn In order to get proper justification and filling of paragraphs in typeset output, SGML-tools includes the ­ entity. This becomes an optional or `soft' hyphen in back ends like latex2e for which this is neaningful. The bracketing tag <file> can be used to surround filenames in running text. It effectively inserts soft hyphens after each slash in the filename. One of the advantages of using the <url> and <htmlurl> tags is that they do likewise for long URLs. 44.. FFoorrmmaattttiinngg SSGGMMLL DDooccuummeennttss Let's say you have the SGML document foo.sgml, which you want to format. Here is a general overview of formatting the document for different output. For a complete list of options, consult the man pages. 44..11.. CChheecckkiinngg SSGGMMLL SSyynnttaaxx If you just want to capture your errors from the SGML conversion, use the sgmlcheck script. For example. % sgmlcheck foo.sgml If you see no output from an sgmlcheck run other than the ``Processing...'' message, that's good. It means there were no errors. 44..22.. CCrreeaattiinngg PPllaaiinn TTeexxtt OOuuttppuutt If you want to produce plain text, use the command: % sgml2txt foo.sgml You can also create groff source for man pages, which can be formatted with groff -man. To do this, do the following: % sgml2txt --man foo.sgml 44..33.. CCrreeaattiinngg LLaaTTeeXX,, DDVVII oorr PPoossttSSccrriipptt OOuuttppuutt To create a LaTeX documents from the SGML source file, simply run: % sgml2latex foo.sgml If you want to produce PostScript output (via dvips), use the -p option: % sgml2latex --output=ps foo.sgml Or you can produce a DVI file: % sgml2latex --output=dvi foo.sgml 44..44.. CCrreeaattiinngg HHTTMMLL OOuuttppuutt If you want to produce HTML output, do this: % sgml2html --imagebuttons foo.sgml This will produce foo.html, as well as foo-1.html, foo-2.html, and so on -- one file for each section of the document. Run your WWW browser on foo.html, which is the top level file. You must make sure that all of the HTML files generated from your document are all installed in the directory, as they reference each other with local URLs. The --imagebuttons option tells sgml2html to use graphic arrows as navigation buttons. The names of these icons are "next.gif", "prev.gif", and "toc.gif", and the SGML-tools system supplies appropriate GIFs in its library directory. If you use sgml2html without the -img flag, HTML documents will by default have the English labels ``Previous'', ``Next'', and ``Table of Contents'' for navigation. If you specify one of the accepted language codes in a --language option, however, the labels will be given in that language. 44..55.. CCrreeaattiinngg GGNNUU IInnffoo OOuuttppuutt If you want to format your file for the GNU info browser, just run the following command: % sgml2info foo.sgml 44..66.. CCrreeaattiinngg LLyyXX OOuuttppuutt For LyX output, use the the command: % sgml2lyx foo.sgml 44..77.. CCrreeaattiinngg RRTTFF OOuuttppuutt If you want to produce RTF output, run the command: % sgml2rtf foo.sgml This will produce foo.rtf, as well as foo-1.rtf, foo-2.rtf, and so on---one file for each section of the document. 55.. IInntteerrnnaattiioonnaalliizzaattiioonn SSuuppppoorrtt The ISO 8859-1 (latin1) character set may be used for international characters in plain text, LaTeX, HTML, LyX, and RTF output (GNU info support for ISO 8859-1 may be possible in the future). To use this feature, give the formatting scripts the --charset=latin flag, for example: % sgml2txt --charset=latin foo.sgml You also can use ISO 8859-1 characters in the SGML source, they will automatically be translated to the proper escape codes for the corre- sponding output format. 66.. HHooww SSGGMMLL--TToooollss WWoorrkkss Technically, the tags and conventions we've explored in previous sections of this use's guide are what is called a _m_a_r_k_u_p _l_a_n_g_u_a_g_e -- a way to embed formatting information in a document so that programs can do useful things with it. HTML, Tex, and Unix manual-page macros are well-known examples of markup languages. 66..11.. OOvveerrvviieeww ooff SSGGMMLL SGML-tools is so called because it uses a way of describing markup languages called SGML (Standard Generalized Markup Language). SGML itself doesn't describe a markup language; rather, it's a language for writing specifications for markup languages. The reason SGML is useful is that an SGML markup specification for a language can be used to generate programs that "know" that language with much less effort (and a much lower bugginess rate!) than if they had to be coded by hand. In SGML jargon, a markup language specification is called a ``DTD'' (Document Type Definition). A DTD allows you to specify the _s_t_r_u_c_t_u_r_e of a kind of document---that is, what parts, in what order, make up a document of that kind. Given a DTD, an SGML parser can check a document for correctness. An SGML-parser/DTD combination can also make it easy to write programs that translate that structure into another markup language -- and this is exactly how SGML-tools actually works. SGML-Tools provides a SGML DTD called ``linuxdoc'' and a set of ``replacement files'' which convert the linuxdoc documents to groff, LaTeX, HTML, GNU info, LyX, and RTF source. This is why the example document has a magic cookie at thtop of it that says "linuxdoc system"; that is how one tells an SGML parser what DTD to use. Actually, SGML-tools provides a couple of closely related DTDs. But the ones other than linuxdoc are still experimental, and you probably do not want to try working with them unless you are an SGML-tools guru. If you are an SGML guru, you may find it interesting to know that the SGML-Tools DTDs are based heavily on the QWERTZ DTD by Tom Gordon, thomas.gordon@gmd.de. If you are not an SGML guru, you may not know that HTML (the markup language used on the World Wide Web) is itself sefined by a DTD. 66..22.. HHooww SSGGMMLL WWoorrkkss An SGML DTD like linuxdoc specifies the names of ``elements'' within a document type. An element is just a bit of structure---like a section, a subsection, a paragraph, or even something smaller like _e_m_p_h_a_s_i_z_e_d _t_e_x_t. Unlike in LaTeX, however, these elements are not in any way intrinsic to SGML itself. The linuxdoc DTD happens to define elements that look a lot like their LaTeX counterparts---you have sections, subsections, verbatim ``environments'', and so forth. However, using SGML you can define any kind of structure for the document that you like. In a way, SGML is like low-level TeX, while the linuxdoc DTD is like LaTeX. Don't be confused by this analogy. SGML is _n_o_t a text-formatting system. There is no ``SGML formatter'' per se. SGML source is _o_n_l_y converted to other formats for processing. Furthermore, SGML itself is used only to specify the document structure. There are no text- formatting facilities or ``macros'' intrinsic to SGML itself. All of those things are defined within the DTD. You can't use SGML without a DTD, a DTD defines what SGML does. 66..33.. WWhhaatt HHaappppeennss WWhheenn SSGGMMLL--TToooollss PPrroocceesssseess AA DDooccuummeenntt Here's how processing a document with SGML-Tools works. First, you need a DTD, which sets up the structure of the document. A small portion of the normal (linuxdoc) DTD looks like this: <!element article - - (titlepag, header?, toc?, lof?, lot?, p*, sect*, (appendix, sect+)?, biblio?) +(footnote)> This part sets up the overall structure for an ``article'', which is like a ``documentstyle'' within LaTeX. The article consists of a titlepage (titlepag), an optional header (header), an optional table of contents (toc), optional lists of figures (lof) and tables (lot), any number of paragraphs (p), any number of top-level sections (sect), optional appendices (appendix), an optional bibliography (biblio) and footnotes (footnote). As you can see, the DTD doesn't say anything about how the document should be formatted or what it should look like. It just defines what parts make up the document. Elsewhere in the DTD the structure of the titlepag, header, sect, and other elements are defined. You don't need to know anything about the syntax of the DTD in order to write documents. We're just presenting it here so you know what it looks like and what it does. You _d_o need to be familiar with the document _s_t_r_u_c_t_u_r_e that the DTD defines. If not, you might violate the structure when attempting to write a document, and be very confused about the resulting error messages. The next step is to write a document using the structure defined by the DTD. Again, the linuxdoc DTD makes documents look a lot like LaTeX or HTML -- it's very easy to follow. In SGML jargon a single document written using a particular DTD is known as an ``instance'' of that DTD. In order to translate the SGML source into another format (such as LaTeX or groff) for processing, the SGML source (the document that you wrote) is _p_a_r_s_e_d along with the DTD by the SGML _p_a_r_s_e_r. SGML-Tools uses the nsgmls parser by James Clark, jjc@jclark.com, who also happens to be the author of groff. We're in good hands. The parser (sgmls) simply picks through your document and verifies that it follows the structure set forth by the DTD. It also spits out a more explicit form of your document, with all ``macros'' and elements expanded, which is understood by sgmlsasp, the next part of the process. sgmlsasp is responsible for converting the output of sgmls to another format (such as LaTeX). It does this using _r_e_p_l_a_c_e_m_e_n_t _f_i_l_e_s, which describe how to convert elements in the original SGML document into corresponding source in the ``target'' format (such as LaTeX or groff). For example, part of the replacement file for LaTeX looks like: <itemize> + "\\begin{itemize} + </itemize> + "\\end{itemize} + Which says that whenever you begin an itemize element in the SGML source, it should be replaced with \begin{itemize} in the LaTeX source. (As I said, elements in the DTD are very similar to their LaTeX counterparts). So, to convert the SGML to another format, all you have to do is write a new replacement file for that format that gives the appropriate analogies to the SGML elements in that new format. In practice, it's not that simple---for example, if you're trying to convert to a format that isn't structured at all like your DTD, you're going to have trouble. In any case, it's much easier to do than writing individual parsers and translators for many kinds of output formats; SGML provides a generalized system for converting one source to many formats. Once sgmlsasp has completed its work, you have LaTeX source which corresponds to your original SGML document, which you can format using LaTeX as you normally would. 66..44.. FFuurrtthheerr IInnffoorrmmaattiioonn +o The QWERTZ User's Guide is available from ftp://ftp.cs.cornell.edu/pub/mdw/SGML. QWERTZ (and hence, SGML- Tools) supports many features such as mathematical formulae, tables, figures, and so forth. If you'd like to write general documentation in SGML, I suggest using the original QWERTZ DTD instead of the hacked-up linuxdoc DTD, which I've modified for use particularly by the Linux HOWTOs and other such documentation. +o Tom Gordon's original QWERTZ tools can be found at ftp://ftp.gmd.de/GMD/sgml. +o More information on SGML can be found at the following WWW pages: 1. SGML and the Web <http://www.w3.org/hypertext/WWW/MarkUp/SGML/> 2. SGML Web Page <http://www.sil.org/sgml/sgml.html> 3. Yahoo's SGML Page <http://www.yahoo.com/Computers_and_Internet/Software/Data_Formats/SGML> +o James Clark's sgmls parser, and it's successor nsgmls and other tools can be found at ftp://ftp.jclark.com and at James Clark's WWW Page <http://www.jclark.com>. +o The emacs psgml package can be found at ftp://ftp.lysator.liu.se/pub/sgml. This package provides a lot of SGML functionality. +o You can join the SGML-Tools mailing list by sending mail to majordomo@via.ecp.fr with subscribe sgml-tools in the message body. The list address is sgml-tools@via.ecp.fr. +o More information on LyX can be found at the LyX WWW Page <http://wsiserv.informatik.uni-tuebingen.de/~ettrich/>. LyX is a high-level word processor frontend to LaTeX. Quasi-WYSIWYG interface, many LaTeX styles and layouts automatically generated. Speeds up learning LaTeX and makes complicated layouts easy and intuitive.