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diff --git a/en_US.ISO8859-1/books/fdp-primer/sgml-primer/chapter.sgml b/en_US.ISO8859-1/books/fdp-primer/sgml-primer/chapter.sgml deleted file mode 100644 index e6378df431..0000000000 --- a/en_US.ISO8859-1/books/fdp-primer/sgml-primer/chapter.sgml +++ /dev/null @@ -1,1556 +0,0 @@ -<!-- Copyright (c) 1998, 1999 Nik Clayton, All rights reserved. - - Redistribution and use in source (SGML DocBook) and 'compiled' forms - (SGML, HTML, PDF, PostScript, RTF and so forth) with or without - modification, are permitted provided that the following conditions - are met: - - 1. Redistributions of source code (SGML DocBook) must retain the above - copyright notice, this list of conditions and the following - disclaimer as the first lines of this file unmodified. - - 2. Redistributions in compiled form (transformed to other DTDs, - converted to PDF, PostScript, RTF and other formats) must reproduce - the above copyright notice, this list of conditions and the - following disclaimer in the documentation and/or other materials - provided with the distribution. - - THIS DOCUMENTATION IS PROVIDED BY NIK CLAYTON "AS IS" AND ANY EXPRESS OR - IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES - OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE - DISCLAIMED. IN NO EVENT SHALL NIK CLAYTON BE LIABLE FOR ANY DIRECT, - INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES - (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR - SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) - HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, - STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN - ANY WAY OUT OF THE USE OF THIS DOCUMENTATION, EVEN IF ADVISED OF THE - POSSIBILITY OF SUCH DAMAGE. - - $FreeBSD: doc/en_US.ISO_8859-1/books/fdp-primer/sgml-primer/chapter.sgml,v 1.16 2001/04/09 00:33:47 dd Exp $ ---> - -<chapter id="sgml-primer"> - <title>SGML Primer</title> - - <para>The majority of FDP documentation is written in applications of - SGML. This chapter explains exactly what that means, how to read - and understand the source to the documentation, and the sort of SGML - tricks you will see used in the documentation.</para> - - <para>Portions of this section were inspired by Mark Galassi's <ulink - url="http://nis-www.lanl.gov/~rosalia/mydocs/docbook-intro/docbook-intro.html">Get Going With DocBook</ulink>.</para> - - <sect1> - <title>Overview</title> - - <para>Way back when, electronic text was simple to deal with. Admittedly, - you had to know which character set your document was written in (ASCII, - EBCDIC, or one of a number of others) but that was about it. Text was - text, and what you saw really was what you got. No frills, no - formatting, no intelligence.</para> - - <para>Inevitably, this was not enough. Once you have text in a - machine-usable format, you expect machines to be able to use it and - manipulate it intelligently. You would like to indicate that certain - phrases should be emphasised, or added to a glossary, or be hyperlinks. - You might want filenames to be shown in a “typewriter” style - font for viewing on screen, but as “italics” when printed, - or any of a myriad of other options for presentation.</para> - - <para>It was once hoped that Artificial Intelligence (AI) would make this - easy. Your computer would read in the document and automatically - identify key phrases, filenames, text that the reader should type in, - examples, and more. Unfortunately, real life has not happened quite - like that, and our computers require some assistance before they can - meaningfully process our text.</para> - - <para>More precisely, they need help identifying what is what. You or I - can look at - - <blockquote> - <para>To remove <filename>/tmp/foo</filename> use &man.rm.1;.</para> - - <screen>&prompt.user; <userinput>rm /tmp/foo</userinput></screen> - </blockquote> - - and easily see which parts are filenames, which are commands to be typed - in, which parts are references to manual pages, and so on. But the - computer processing the document can not. For this we need - markup.</para> - - <para>“Markup” is commonly used to describe “adding - value” or “increasing cost”. The term takes on both - these meanings when applied to text. Markup is additional text included - in the document, distinguished from the document's content in some way, - so that programs that process the document can read the markup and use - it when making decisions about the document. Editors can hide the - markup from the user, so the user is not distracted by it.</para> - - <para>The extra information stored in the markup <emphasis>adds - value</emphasis> to the document. Adding the markup to the document - must typically be done by a person—after all, if computers could - recognise the text sufficiently well to add the markup then there would - be no need to add it in the first place. This <emphasis>increases the - cost</emphasis> (i.e., the effort required) to create the - document.</para> - - <para>The previous example is actually represented in this document like - this;</para> - - <programlisting><![ CDATA [ -<para>To remove <filename>/tmp/foo</filename> use &man.rm.1;.</para> - -<screen>&prompt.user; <userinput>rm /tmp/foo</userinput></screen>]]></programlisting> - - <para>As you can see, the markup is clearly separate from the - content.</para> - - <para>Obviously, if you are going to use markup you need to define what - your markup means, and how it should be interpreted. You will need a - markup language that you can follow when marking up your - documents.</para> - - <para>Of course, one markup language might not be enough. A markup - language for technical documentation has very different requirements - than a markup language that was to be used for cookery recipes. This, - in turn, would be very different from a markup language used to describe - poetry. What you really need is a first language that you use to write - these other markup languages. A <emphasis>meta markup - language</emphasis>.</para> - - <para>This is exactly what the Standard Generalised Markup Language (SGML) - is. Many markup languages have been written in SGML, including the two - most used by the FDP, HTML and DocBook.</para> - - <para>Each language definition is more properly called a Document Type - Definition (DTD). The DTD specifies the name of the elements that can - be used, what order they appear in (and whether some markup can be used - inside other markup) and related information. A DTD is sometimes - referred to as an <emphasis>application</emphasis> of SGML.</para> - - <para id="sgml-primer-validating">A DTD is a <emphasis>complete</emphasis> - specification of all the elements that are allowed to appear, the order - in which they should appear, which elements are mandatory, which are - optional, and so forth. This makes it possible to write an SGML - <emphasis>parser</emphasis> which reads in both the DTD and a document - which claims to conform to the DTD. The parser can then confirm whether - or not all the elements required by the DTD are in the document in the - right order, and whether there are any errors in the markup. This is - normally referred to as <quote>validating the document</quote>.</para> - - <note> - <para>This processing simply confirms that the choice of elements, their - ordering, and so on, conforms to that listed in the DTD. It does - <emphasis>not</emphasis> check that you have used - <emphasis>appropriate</emphasis> markup for the content. If you were - to try and mark up all the filenames in your document as function - names, the parser would not flag this as an error (assuming, of - course, that your DTD defines elements for filenames and functions, - and that they are allowed to appear in the same place).</para> - </note> - - <para>It is likely that most of your contributions to the Documentation - Project will consist of content marked up in either HTML or DocBook, - rather than alterations to the DTDs. For this reason this book will - not touch on how to write a DTD.</para> - </sect1> - - <sect1 id="sgml-primer-elements"> - <title>Elements, tags, and attributes</title> - - <para>All the DTDs written in SGML share certain characteristics. This is - hardly surprising, as the philosophy behind SGML will inevitably show - through. One of the most obvious manifestations of this philisophy is - that of <emphasis>content</emphasis> and - <emphasis>elements</emphasis>.</para> - - <para>Your documentation (whether it is a single web page, or a lengthy - book) is considered to consist of content. This content is then divided - (and further subdivided) into elements. The purpose of adding markup is - to name and identify the boundaries of these elements for further - processing.</para> - - <para>For example, consider a typical book. At the very top level, the - book is itself an element. This “book” element obviously - contains chapters, which can be considered to be elements in their own - right. Each chapter will contain more elements, such as paragraphs, - quotations, and footnotes. Each paragraph might contain further - elements, identifying content that was direct speech, or the name of a - character in the story.</para> - - <para>You might like to think of this as “chunking” content. - At the very top level you have one chunk, the book. Look a little - deeper, and you have more chunks, the individual chapters. These are - chunked further into paragraphs, footnotes, character names, and so - on.</para> - - <para>Notice how you can make this differentation between different - elements of the content without resorting to any SGML terms. It really - is surprisingly straightforward. You could do this with a highlighter - pen and a printout of the book, using different colours to indicate - different chunks of content.</para> - - <para>Of course, we do not have an electronic highlighter pen, so we need - some other way of indicating which element each piece of content belongs - to. In languages written in SGML (HTML, DocBook, et al) this is done by - means of <emphasis>tags</emphasis>.</para> - - <para>A tag is used to identify where a particular element starts, and - where the element ends. <emphasis>The tag is not part of the element - itself</emphasis>. Because each DTD was normally written to mark up - specific types of information, each one will recognise different - elements, and will therefore have different names for the tags.</para> - - <para>For an element called <replaceable>element-name</replaceable> the - start tag will normally look like - <literal><<replaceable>element-name</replaceable>></literal>. The - corresponding closing tag for this element is - <literal></<replaceable>element-name</replaceable>></literal>.</para> - - <example> - <title>Using an element (start and end tags)</title> - - <para>HTML has an element for indicating that the content enclosed by - the element is a paragraph, called <literal>p</literal>. This - element has both start and end tags.</para> - - <programlisting><![ CDATA [<p>This is a paragraph. It starts with the start tag for - the 'p' element, and it will end with the end tag for the 'p' - element.</p> - -<p>This is another paragraph. But this one is much shorter.</p>]]></programlisting> - </example> - - <para>Not all elements require an end tag. Some elements have no content. - For example, in HTML you can indicate that you want a horizontal line to - appear in the document. Obviously, this line has no content, so just - the start tag is required for this element.</para> - - <example> - <title>Using an element (start tag only)</title> - - <para>HTML has an element for indicating a horizontal rule, called - <literal>hr</literal>. This element does not wrap content, so only - has a start tag.</para> - - <programlisting><![ CDATA [<p>This is a paragraph.</p> - -<hr> - -<p>This is another paragraph. A horizontal rule separates this - from the previous paragraph.</p>]]></programlisting> - </example> - - <para>If it is not obvious by now, elements can contain other elements. - In the book example earlier, the book element contained all the chapter - elements, which in turn contained all the paragraph elements, and so - on.</para> - - <example> - <title>Elements within elements; <sgmltag>em</sgmltag></title> - - <programlisting><![ CDATA [<p>This is a simple <em>paragraph</em> where some - of the <em>words</em> have been <em>emphasised</em>.</p>]]></programlisting> - </example> - - <para>The DTD will specify the rules detailing which elements can contain - other elements, and exactly what they can contain.</para> - - <important> - <para>People often confuse the terms tags and elements, and use the - terms as if they were interchangeable. They are not.</para> - - <para>An element is a conceptual part of your document. An element has - a defined start and end. The tags mark where the element starts and - end.</para> - - <para>When this document (or anyone else knowledgable about SGML) refers - to “the <p> tag” they mean the literal text - consisting of the three characters <literal><</literal>, - <literal>p</literal>, and <literal>></literal>. But the phrase - “the <p> element” refers to the whole - element.</para> - - <para>This distinction <emphasis>is</emphasis> very subtle. But keep it - in mind.</para> - </important> - - <para>Elements can have attributes. An attribute has a name and a value, - and is used for adding extra information to the element. This might be - information that indicates how the content should be rendered, or might - be something that uniquely identifies that occurence of the element, or - it might be something else.</para> - - <para>An element's attributes are written <emphasis>inside</emphasis> the - start tag for that element, and take the form - <literal><replaceable>attribute-name</replaceable>="<replaceable>attribute-value</replaceable>"</literal>.</para> - - <para>In sufficiently recent versions of HTML, the <sgmltag>p</sgmltag> - element has an attribute called <literal>align</literal>, which suggests - an alignment (justification) for the paragraph to the program displaying - the HTML.</para> - - <para>The <literal>align</literal> attribute can take one of four defined - values, <literal>left</literal>, <literal>center</literal>, - <literal>right</literal> and <literal>justify</literal>. If the - attribute is not specified then the default is - <literal>left</literal>.</para> - - <example> - <title>Using an element with an attribute</title> - - <programlisting><![ CDATA [<p align="left">The inclusion of the align attribute - on this paragraph was superfluous, since the default is left.</p> - -<p align="center">This may appear in the center.</p>]]></programlisting> - </example> - - <para>Some attributes will only take specific values, such as - <literal>left</literal> or <literal>justify</literal>. Others will - allow you to enter anything you want. If you need to include quotes - (<literal>"</literal>) within an attribute then use single quotes around - the attribute value.</para> - - <example> - <title>Single quotes around attributes</title> - - <programlisting><![ CDATA [<p align='right'>I'm on the right!</p>]]></programlisting> - </example> - - <para>Sometimes you do not need to use quotes around attribute values at - all. However, the rules for doing this are subtle, and it is far - simpler just to <emphasis>always</emphasis> quote your attribute - values.</para> - - <sect2> - <title>For you to do…</title> - - <para>In order to run the examples in this document you will need to - install some software on your system and ensure that an environment - variable is set correctly.</para> - - <procedure> - <step> - <para>Download and install <filename>textproc/docproj</filename> - from the FreeBSD ports system. This is a - <emphasis>meta-port</emphasis> that should download and install - all of the programs and supporting files that are used by the - Documentation Project.</para> - </step> - - <step> - <para>Add lines to your shell startup files to set - <envar>SGML_CATALOG_FILES</envar>.</para> - - <example id="sgml-primer-envars"> - <title><filename>.profile</filename>, for &man.sh.1; and - &man.bash.1; users</title> - - <programlisting>SGML_ROOT=/usr/local/share/sgml -SGML_CATALOG_FILES=${SGML_ROOT}/jade/catalog -SGML_CATALOG_FILES=${SGML_ROOT}/iso8879/catalog:$SGML_CATALOG_FILES -SGML_CATALOG_FILES=${SGML_ROOT}/html/catalog:$SGML_CATALOG_FILES -SGML_CATALOG_FILES=${SGML_ROOT}/docbook/catalog:$SGML_CATALOG_FILES -export SGML_CATALOG_FILES</programlisting> - </example> - - <example> - <title><filename>.login</filename>, for &man.csh.1; and - &man.tcsh.1; users</title> - - <programlisting>setenv SGML_ROOT /usr/local/share/sgml -setenv SGML_CATALOG_FILES ${SGML_ROOT}/jade/catalog -setenv SGML_CATALOG_FILES ${SGML_ROOT}/iso8879/catalog:$SGML_CATALOG_FILES -setenv SGML_CATALOG_FILES ${SGML_ROOT}/html/catalog:$SGML_CATALOG_FILES -setenv SGML_CATALOG_FILES ${SGML_ROOT}/docbook/catalog:$SGML_CATALOG_FILES</programlisting> - </example> - - <para>Then either log out, and log back in again, or run those - commands from the command line to set the variable values.</para> - </step> - </procedure> - - <procedure> - <step> - <para>Create <filename>example.sgml</filename>, and enter the - following text;</para> - - <programlisting><![ CDATA [<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> - -<html> - <head> - <title>An example HTML file</title> - </head> - - <body> - <p>This is a paragraph containing some text.</p> - - <p>This paragraph contains some more text.</p> - - <p align="right">This paragraph might be right-justified.</p> - </body> -</html>]]></programlisting> - </step> - - <step> - <para>Try and validate this file using an SGML parser.</para> - - <para>Part of <filename>textproc/docproj</filename> is the - &man.nsgmls.1; <link linkend="sgml-primer-validating">validating - parser</link>. Normally, &man.nsgmls.1; reads in a document - marked up according to an SGML DTD and returns a copy of the - document's Element Structure Information Set (ESIS, but that is - not important right now).</para> - - <para>However, when &man.nsgmls.1; is given the <option>-s</option> - parameter, &man.nsgmls.1; will suppress its normal output, and - just print error messages. This makes it a useful way to check to - see if your document is valid or not.</para> - - <para>Use &man.nsgmls.1; to check that your document is - valid;</para> - - <screen>&prompt.user; <userinput>nsgmls -s example.sgml</userinput></screen> - - <para>As you will see, &man.nsgmls.1; returns without displaying any - output. This means that your document validated - successfully.</para> - </step> - - <step> - <para>See what happens when required elements are omitted. Try - removing the <sgmltag>title</sgmltag> and - <sgmltag>/title</sgmltag> tags, and re-run the validation.</para> - - <screen>&prompt.user; <userinput>nsgmls -s example.sgml</userinput> -nsgmls:example.sgml:5:4:E: character data is not allowed here -nsgmls:example.sgml:6:8:E: end tag for "HEAD" which is not finished</screen> - - <para>The error output from &man.nsgmls.1; is organised into - colon-separated groups, or columns.</para> - - <informaltable frame="none"> - <tgroup cols="2"> - <thead> - <row> - <entry>Column</entry> - <entry>Meaning</entry> - </row> - </thead> - - <tbody> - <row> - <entry>1</entry> - <entry>The name of the program generating the error. This - will always be <literal>nsgmls</literal>.</entry> - </row> - - <row> - <entry>2</entry> - <entry>The name of the file that contains the error.</entry> - </row> - - <row> - <entry>3</entry> - <entry>Line number where the error appears.</entry> - </row> - - <row> - <entry>4</entry> - <entry>Column number where the error appears.</entry> - </row> - - <row> - <entry>5</entry> - <entry>A one letter code indicating the nature of the - message. <literal>I</literal> indicates an informational - message, <literal>W</literal> is for warnings, and - <literal>E</literal> is for errors<footnote> - <para>It is not always the fifth column either. - <command>nsgmls -sv</command> displays - <literal>nsgmls:I: SP version "1.3"</literal> - (depending on the installed version). As you can see, - this is an informational message.</para> - </footnote>, and <literal>X</literal> is for - cross-references. As you can see, these messages are - errors.</entry> - </row> - - <row> - <entry>6</entry> - <entry>The text of the error message.</entry> - </row> - </tbody> - </tgroup> - </informaltable> - - <para>Simply omitting the <sgmltag>title</sgmltag> tags has - generated 2 different errors.</para> - - <para>The first error indicates that content (in this case, - characters, rather than the start tag for an element) has occured - where the SGML parser was expecting something else. In this case, - the parser was expecting to see one of the start tags for elements - that are valid inside <sgmltag>head</sgmltag> (such as - <sgmltag>title</sgmltag>).</para> - - <para>The second error is because <sgmltag>head</sgmltag> elements - <emphasis>must</emphasis> contain a <sgmltag>title</sgmltag> - element. Because it does not &man.nsgmls.1; considers that the - element has not been properly finished. However, the closing tag - indicates that the element has been closed before it has been - finished.</para> - </step> - - <step> - <para>Put the <literal>title</literal> element back in.</para> - </step> - </procedure> - </sect2> - </sect1> - - <sect1 id="sgml-primer-doctype-declaration"> - <title>The DOCTYPE declaration</title> - - <para>The beginning of each document that you write must specify the name - of the DTD that the document conforms to. This is so that SGML parsers - can determine the DTD and ensure that the document does conform to - it.</para> - - <para>This information is generally expressed on one line, in the DOCTYPE - declaration.</para> - - <para>A typical declaration for a document written to conform with version - 4.0 of the HTML DTD looks like this;</para> - - <programlisting><![ CDATA [<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN">]]></programlisting> - - <para>That line contains a number of different components.</para> - - <variablelist> - <varlistentry> - <term><literal><!</literal></term> - - <listitem> - <para>Is the <emphasis>indicator</emphasis> that indicates that this - is an SGML declaration. This line is declaring the document type. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>DOCTYPE</literal></term> - - <listitem> - <para>Shows that this is an SGML declaration for the document - type.</para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>html</literal></term> - - <listitem> - <para>Names the first <link linkend="sgml-primer-elements">element</link> that - will appear in the document.</para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>PUBLIC "-//W3C//DTD HTML 4.0//EN"</literal></term> - - <listitem> - <para>Lists the Formal Public Identifier (FPI)<indexterm> - <primary>Formal Public Identifier</primary> - </indexterm> - for the DTD that this - document conforms to. Your SGML parser will use this to find the - correct DTD when processing this document.</para> - - <para><literal>PUBLIC</literal> is not a part of the FPI, but - indicates to the SGML processor how to find the DTD referenced in - the FPI. Other ways of telling the SGML parser how to find the - DTD are shown <link - linkend="sgml-primer-fpi-alternatives">later</link>.</para> - </listitem> - </varlistentry> - - <varlistentry> - <term><literal>></literal></term> - - <listitem> - <para>Returns to the document.</para> - </listitem> - </varlistentry> - </variablelist> - - <sect2> - <title>Formal Public Identifiers (FPIs)<indexterm significance="preferred"> - <primary>Formal Public Identifier</primary> - </indexterm> -</title> - - <note> - <para>You don't need to know this, but it's useful background, and - might help you debug problems when your SGML processor can't locate - the DTD you are using.</para> - </note> - - <para>FPIs must follow a specific syntax. This syntax is as - follows;</para> - - <programlisting>"<replaceable>Owner</replaceable>//<replaceable>Keyword</replaceable> <replaceable>Description</replaceable>//<replaceable>Language</replaceable>"</programlisting> - - <variablelist> - <varlistentry> - <term><replaceable>Owner</replaceable></term> - - <listitem> - <para>This indicates the owner of the FPI.</para> - - <para>If this string starts with “ISO” then this is an - ISO owned FPI. For example, the FPI <literal>"ISO - 8879:1986//ENTITIES Greek Symbols//EN"</literal> lists - <literal>ISO 8879:1986</literal> as being the owner for the set - of entities for greek symbols. ISO 8879:1986 is the ISO number - for the SGML standard.</para> - - <para>Otherwise, this string will either look like - <literal>-//<replaceable>Owner</replaceable></literal> or - <literal>+//<replaceable>Owner</replaceable></literal> (notice - the only difference is the leading <literal>+</literal> or - <literal>-</literal>).</para> - - <para>If the string starts with <literal>-</literal> then the - owner information is unregistered, with a <literal>+</literal> - it identifies it as being registered.</para> - - <para>ISO 9070:1991 defines how registered names are generated; it - might be derived from the number of an ISO publication, an ISBN - code, or an organisation code assigned according to ISO 6523. - In addition, a registration authority could be created in order - to assign registered names. The ISO council delegated this to - the American National Standards Institute (ANSI).</para> - - <para>Because the FreeBSD Project hasn't been registered the - owner string is <literal>-//FreeBSD</literal>. And as you can - see, the W3C are not a registered owner either.</para> - </listitem> - </varlistentry> - - <varlistentry> - <term><replaceable>Keyword</replaceable></term> - - <listitem> - <para>There are several keywords that indicate the type of - information in the file. Some of the most common keywords are - <literal>DTD</literal>, <literal>ELEMENT</literal>, - <literal>ENTITIES</literal>, and <literal>TEXT</literal>. - <literal>DTD</literal> is used only for DTD files, - <literal>ELEMENT</literal> is usually used for DTD fragments - that contain only entity or element declarations. - <literal>TEXT</literal> is used for SGML content (text and - tags).</para> - </listitem> - </varlistentry> - - <varlistentry> - <term><replaceable>Description</replaceable></term> - - <listitem> - <para>Any description you want to supply for the contents of this - file. This may include version numbers or any short text that - is meaningful to you and unique for the SGML system.</para> - </listitem> - </varlistentry> - - <varlistentry> - <term><replaceable>Language</replaceable></term> - - <listitem> - <para>This is an ISO two-character code that identifies the native - language for the file. <literal>EN</literal> is used for - English.</para> - </listitem> - </varlistentry> - </variablelist> - - <sect3> - <title><filename>catalog</filename> files</title> - - <para>If you use the syntax above and try and process this document - using an SGML processor, the processor will need to have some way of - turning the FPI into the name of the file on your computer that - contains the DTD.</para> - - <para>In order to do this it can use a catalog file. A catalog file - (typically called <filename>catalog</filename>) contains lines that - map FPIs to filenames. For example, if the catalog file contained - the line;</para> - - <programlisting>PUBLIC "-//W3C//DTD HTML 4.0//EN" "4.0/strict.dtd"</programlisting> - - <para>The SGML processor would know to look up the DTD from - <filename>strict.dtd</filename> in the <filename>4.0</filename> - subdirectory of whichever directory held the - <filename>catalog</filename> file that contained that line.</para> - - <para>Look at the contents of - <filename>/usr/local/share/sgml/html/catalog</filename>. This is - the catalog file for the HTML DTDs that will have been installed as - part of the <filename>textproc/docproj</filename> port.</para> - </sect3> - - <sect3> - <title><envar>SGML_CATALOG_FILES</envar></title> - - <para>In order to locate a <filename>catalog</filename> file, your - SGML processor will need to know where to look. Many of them - feature command line parameters for specifying the path to one or - more catalogs.</para> - - <para>In addition, you can set <envar>SGML_CATALOG_FILES</envar> to - point to the files. This environment variable should consist of a - colon-separated list of catalog files (including their full - path).</para> - - <para>Typically, you will want to include the following files;</para> - - <itemizedlist> - <listitem> - <para><filename>/usr/local/share/sgml/docbook/catalog</filename></para> - </listitem> - - <listitem> - <para><filename>/usr/local/share/sgml/html/catalog</filename></para> - </listitem> - - <listitem> - <para><filename>/usr/local/share/sgml/iso8879/catalog</filename></para> - </listitem> - - <listitem> - <para><filename>/usr/local/share/sgml/jade/catalog</filename></para> - </listitem> - </itemizedlist> - - <para>You should <link linkend="sgml-primer-envars">already have done - this</link>.</para> - </sect3> - </sect2> - - <sect2 id="sgml-primer-fpi-alternatives"> - <title>Alternatives to FPIs</title> - - <para>Instead of using an FPI to indicate the DTD that the document - conforms to (and therefore, which file on the system contains the DTD) - you can explicitly specify the name of the file.</para> - - <para>The syntax for this is slightly different:</para> - - <programlisting><![ CDATA [<!DOCTYPE html SYSTEM "/path/to/file.dtd">]]></programlisting> - - <para>The <literal>SYSTEM</literal> keyword indicates that the SGML - processor should locate the DTD in a system specific fashion. This - typically (but not always) means the DTD will be provided as a - filename.</para> - - <para>Using FPIs is preferred for reasons of portability. You don't - want to have to ship a copy of the DTD around with your document, and - if you used the <literal>SYSTEM</literal> identifier then everyone - would need to keep their DTDs in the same place.</para> - </sect2> - </sect1> - - <sect1 id="sgml-primer-sgml-escape"> - <title>Escaping back to SGML</title> - - <para>Earlier in this primer I said that SGML is only used when writing a - DTD. This is not strictly true. There is certain SGML syntax that you - will want to be able to use within your documents. For example, - comments can be included in your document, and will be ignored by the - parser. Comments are entered using SGML syntax. Other uses for SGML - syntax in your document will be shown later too.</para> - - <para>Obviously, you need some way of indicating to the SGML processor - that the following content is not elements within the document, but is - SGML that the parser should act upon.</para> - - <para>These sections are marked by <literal><! ... ></literal> in - your document. Everything between these delimiters is SGML syntax as - you might find within a DTD.</para> - - <para>As you may just have realised, the <link - linkend="sgml-primer-doctype-declaration">DOCTYPE declaration</link> - is an example of SGML syntax that you need to include in your - document…</para> - </sect1> - - <sect1> - <title>Comments</title> - - <para>Comments are an SGML construction, and are normally only valid - inside a DTD. However, as <xref linkend="sgml-primer-sgml-escape"> - shows, it is possible to use SGML syntax within your document.</para> - - <para>The delimiter for SGML comments is the string - “<literal>--</literal>”. The first occurence of this string - opens a comment, and the second closes it.</para> - - <example> - <title>SGML generic comment</title> - - <programlisting><!-- test comment --></programlisting> - - <programlisting><![ CDATA [ -<!-- This is inside the comment --> - -<!-- This is another comment --> - -<!-- This is one way - of doing multiline comments --> - -<!-- This is another way of -- - -- doing multiline comments -->]]></programlisting> - </example> - - <![ %output.print; [ - <important> - <title>Use 2 dashes</title> - - <para>There is a problem with producing the Postscript and PDF versions - of this document. The above example probably shows just one hyphen - symbol, <literal>-</literal> after the <literal><!</literal> and - before the <literal>></literal>.</para> - - <para>You <emphasis>must</emphasis> use two <literal>-</literal>, - <emphasis>not</emphasis> one. The Postscript and PDF versions have - translated the two <literal>-</literal> in the original to a longer, - more professional <emphasis>em-dash</emphasis>, and broken this - example in the process.</para> - - <para>The HTML, plain text, and RTF versions of this document are not - affected.</para> - </important> - ]]> - - <para>If you have used HTML before you may have been shown different rules - for comments. In particular, you may think that the string - <literal><!--</literal> opens a comment, and it is only closed by - <literal>--></literal>.</para> - - <para>This is <emphasis>not</emphasis> the case. A lot of web browsers - have broken HTML parsers, and will accept that as valid. However, the - SGML parsers used by the Documentation Project are much stricter, and - will reject documents that make that error.</para> - - <example> - <title>Errorneous SGML comments</title> - - <programlisting><![ CDATA [ -<!-- This is in the comment -- - - THIS IS OUTSIDE THE COMMENT! - - -- back inside the comment -->]]></programlisting> - - <para>The SGML parser will treat this as though it were actually;</para> - - <programlisting><!THIS IS OUTSIDE THE COMMENT></programlisting> - - <para>This is not valid SGML, and may give confusing error - messages.</para> - - <programlisting><![ CDATA [<!--------------- This is a very bad idea --------------->]]></programlisting> - - <para>As the example suggests, <emphasis>do not</emphasis> write - comments like that.</para> - - <programlisting><![ CDATA [<!--===================================================-->]]></programlisting> - - <para>That is a (slightly) better approach, but it still potentially - confusing to people new to SGML.</para> - </example> - - <sect2> - <title>For you to do…</title> - - <procedure> - <step> - <para>Add some comments to <filename>example.sgml</filename>, and - check that the file still validates using &man.nsgmls.1;</para> - </step> - - <step> - <para>Add some invalid comments to - <filename>example.sgml</filename>, and see the error messages that - &man.nsgmls.1; gives when it encounters an invalid comment.</para> - </step> - </procedure> - </sect2> - </sect1> - - <sect1> - <title>Entities</title> - - <para>Entities are a mechanism for assigning names to chunks of content. - As an SGML parser processes your document, any entities it finds are - replaced by the content of the entity.</para> - - <para>This is a good way to have re-usable, easily changeable chunks of - content in your SGML documents. It is also the only way to include one - marked up file inside another using SGML.</para> - - <para>There are two types of entities which can be used in two different - situations; <emphasis>general entities</emphasis> and - <emphasis>parameter entities</emphasis>.</para> - - <sect2 id="sgml-primer-general-entities"> - <title>General Entities</title> - - <para>You can not use general entities in an SGML context (although you - define them in one). They can only be used in your document. - Contrast this with <link - linkend="sgml-primer-parameter-entities">parameter - entities</link>.</para> - - <para>Each general entity has a name. When you want to reference a - general entity (and therefore include whatever text it represents in - your document), you write - <literal>&<replaceable>entity-name</replaceable>;</literal>. For - example, suppose you had an entity called - <literal>current.version</literal> which expanded to the current - version number of your product. You could write;</para> - - <programlisting><![ CDATA [<para>The current version of our product is - ¤t.version;.</para>]]></programlisting> - - <para>When the version number changes you can simply change the - definition of the value of the general entity and reprocess your - document.</para> - - <para>You can also use general entities to enter characters that you - could not otherwise include in an SGML document. For example, < - and & can not normally appear in an SGML document. When the SGML - parser sees the < symbol it assumes that a tag (either a start tag - or an end tag) is about to appear, and when it sees the & symbol - it assumes the next text will be the name of an entity.</para> - - <para>Fortunately, you can use the two general entities &lt; and - &amp; whenever you need to include one or other of these </para> - - <para>A general entity can only be defined within an SGML context. - Typically, this is done immediately after the DOCTYPE - declaration.</para> - - <example> - <title>Defining general entities</title> - - <programlisting><![ CDATA [<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN" [ -<!ENTITY current.version "3.0-RELEASE"> -<!ENTITY last.version "2.2.7-RELEASE"> -]>]]></programlisting> - - <para>Notice how the DOCTYPE declaration has been extended by adding a - square bracket at the end of the first line. The two entities are - then defined over the next two lines, before the square bracket is - closed, and then the DOCTYPE declaration is closed.</para> - - <para>The square brackets are necessary to indicate that we are - extending the DTD indicated by the DOCTYPE declaration.</para> - </example> - </sect2> - - <sect2 id="sgml-primer-parameter-entities"> - <title>Parameter entities</title> - - <para>Like <link linkend="sgml-primer-general-entities">general - entities</link>, parameter entities are used to assign names to - reusable chunks of text. However, where as general entities can only - be used within your document, parameter entities can only be used - within an <link linkend="sgml-primer-sgml-escape">SGML - context</link>.</para> - - <para>Parameter entities are defined in a similar way to general - entities. However, instead of using - <literal>&<replaceable>entity-name</replaceable>;</literal> to - refer to them, use - <literal>%<replaceable>entity-name</replaceable>;</literal><footnote> - <para><emphasis>P</emphasis>arameter entities use the - <emphasis>P</emphasis>ercent symbol.</para> - </footnote>. The definition also includes the <literal>%</literal> - between the <literal>ENTITY</literal> keyword and the name of the - entity.</para> - - <example> - <title>Defining parameter entities</title> - - <programlisting><![ CDATA [<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN" [ -<!ENTITY % param.some "some"> -<!ENTITY % param.text "text"> -<!ENTITY % param.new "%param.some more %param.text"> - -<!-- %param.new now contains "some more text" --> -]>]]></programlisting> - </example> - - <para>This may not seem particularly useful. It will be.</para> - </sect2> - - <sect2> - <title>For you to do…</title> - - <procedure> - <step> - <para>Add a general entity to - <filename>example.sgml</filename>.</para> - - <programlisting><![ CDATA [<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" [ -<!ENTITY version "1.1"> -]> - -<html> - <head> - <title>An example HTML file</title> - </head> - - <!-- You might well have some comments in here as well --> - - <body> - <p>This is a paragraph containing some text.</p> - - <p>This paragraph contains some more text.</p> - - <p align="right">This paragraph might be right-justified.</p> - - <p>The current version of this document is: &version;</p> - </body> -</html>]]></programlisting> - </step> - - <step> - <para>Validate the document using &man.nsgmls.1;</para> - </step> - - <step> - <para>Load <filename>example.sgml</filename> into your web browser - (you may need to copy it to <filename>example.html</filename> - before your browser recognises it as an HTML document).</para> - - <para>Unless your browser is very advanced, you won't see the entity - reference <literal>&version;</literal> replaced with the - version number. Most web browsers have very simplistic parsers - which do not handle proper SGML<footnote> - <para>This is a shame. Imagine all the problems and hacks (such - as Server Side Includes) that could be avoided if they - did.</para> - </footnote>.</para> - </step> - - <step> - <para>The solution is to <emphasis>normalise</emphasis> your - document using an SGML normaliser. The normaliser reads in valid - SGML and outputs equally valid SGML which has been transformed in - some way. One of the ways in which the normaliser transforms the - SGML is to expand all the entity references in the document, - replacing the entities with the text that they represent.</para> - - <para>You can use &man.sgmlnorm.1; to do this.</para> - - <screen>&prompt.user; <userinput>sgmlnorm example.sgml > example.html</userinput></screen> - - <para>You should find a normalised (i.e., entity references - expanded) copy of your document in - <filename>example.html</filename>, ready to load into your web - browser.</para> - </step> - - <step> - <para>If you look at the output from &man.sgmlnorm.1; you will see - that it does not include a DOCTYPE declaration at the start. To - include this you need to use the <option>-d</option> - option;</para> - - <screen>&prompt.user; <userinput>sgmlnorm -d example.sgml > example.html</userinput></screen> - </step> - </procedure> - </sect2> - </sect1> - - <sect1> - <title>Using entities to include files</title> - - <para>Entities (both <link - linkend="sgml-primer-general-entities">general</link> and <link - linkend="sgml-primer-parameter-entities">parameter</link>) are - particularly useful when used to include one file inside another.</para> - - <sect2 id="sgml-primer-include-using-gen-entities"> - <title>Using general entities to include files</title> - - <para>Suppose you have some content for an SGML book organised into - files, one file per chapter, called - <filename>chapter1.sgml</filename>, - <filename>chapter2.sgml</filename>, and so forth, with a - <filename>book.sgml</filename> file that will contain these - chapters.</para> - - <para>In order to use the contents of these files as the values for your - entities, you declare them with the <literal>SYSTEM</literal> keyword. - This directs the SGML parser to use the contents of the named file as - the value of the entity.</para> - - <example> - <title>Using general entities to include files</title> - - <programlisting><![ CDATA [<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN" [ -<!ENTITY chapter.1 SYSTEM "chapter1.sgml"> -<!ENTITY chapter.2 SYSTEM "chapter2.sgml"> -<!ENTITY chapter.3 SYSTEM "chapter3.sgml"> -<!-- And so forth --> -]> - -<html> - <!-- Use the entities to load in the chapters --> - - &chapter.1; - &chapter.2; - &chapter.3; -</html>]]></programlisting> - </example> - - <warning> - <para>When using general entities to include other files within a - document, the files being included - (<filename>chapter1.sgml</filename>, - <filename>chapter2.sgml</filename>, and so on) <emphasis>must - not</emphasis> start with a DOCTYPE declaration. This is a syntax - error.</para> - </warning> - </sect2> - - <sect2> - <title>Using parameter entities to include files</title> - - <para>Recall that parameter entities can only be used inside an SGML - context. Why then would you want to include a file within an SGML - context?</para> - - <para>You can use this to ensure that you can reuse your general - entities.</para> - - <para>Suppose that you had many chapters in your document, and you - reused these chapters in two different books, each book organising the - chapters in a different fashion.</para> - - <para>You could list the entities at the top of each book, but this - quickly becomes cumbersome to manage.</para> - - <para>Instead, place the general entity definitions inside one file, - and use a parameter entity to include that file within your - document.</para> - - <example> - <title>Using parameter entities to include files</title> - - <para>First, place your entity definitions in a separate file, called - <filename>chapters.ent</filename>. This file contains the - following;</para> - - <programlisting><![ CDATA [<!ENTITY chapter.1 SYSTEM "chapter1.sgml"> -<!ENTITY chapter.2 SYSTEM "chapter2.sgml"> -<!ENTITY chapter.3 SYSTEM "chapter3.sgml">]]></programlisting> - - <para>Now create a parameter entity to refer to the contents of the - file. Then use the parameter entity to load the file into the - document, which will then make all the general entities available - for use. Then use the general entities as before;</para> - - <programlisting><![ CDATA [<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN" [ -<!-- Define a parameter entity to load in the chapter general entities --> -<!ENTITY % chapters SYSTEM "chapters.ent"> - -<!-- Now use the parameter entity to load in this file --> -%chapters; -]> - -<html> - &chapter.1; - &chapter.2; - &chapter.3; -</html>]]></programlisting> - </example> - </sect2> - - <sect2> - <title>For you to do…</title> - - <sect3> - <title>Use general entities to include files</title> - - <procedure> - <step> - <para>Create three files, <filename>para1.sgml</filename>, - <filename>para2.sgml</filename>, and - <filename>para3.sgml</filename>.</para> - - <para>Put content similar to the following in each file;</para> - - <programlisting><![ CDATA [<p>This is the first paragraph.</p>]]></programlisting> - </step> - - <step> - <para>Edit <filename>example.sgml</filename> so that it looks like - this;</para> - - <programlisting><![ CDATA [<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN" [ -<!ENTITY version "1.1"> -<!ENTITY para1 SYSTEM "para1.sgml"> -<!ENTITY para2 SYSTEM "para2.sgml"> -<!ENTITY para3 SYSTEM "para3.sgml"> -]> - -<html> - <head> - <title>An example HTML file</title> - </head> - - <body> - <p>The current version of this document is: &version;</p> - - ¶1; - ¶2; - ¶3; - </body> -</html>]]></programlisting> - </step> - - <step> - <para>Produce <filename>example.html</filename> by normalising - <filename>example.sgml</filename>.</para> - - <screen>&prompt.user; <userinput>sgmlnorm -d example.sgml > example.html</userinput></screen> - </step> - - <step> - <para>Load <filename>example.html</filename> in to your web - browser, and confirm that the - <filename>para<replaceable>n</replaceable>.sgml</filename> files - have been included in <filename>example.html</filename>.</para> - </step> - </procedure> - </sect3> - - <sect3> - <title>Use parameter entities to include files</title> - - <note> - <para>You must have taken the previous steps first.</para> - </note> - - <procedure> - <step> - <para>Edit <filename>example.sgml</filename> so that it looks like - this;</para> - - <programlisting><![ CDATA [<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN" [ -<!ENTITY % entities SYSTEM "entities.sgml"> %entities; -]> - -<html> - <head> - <title>An example HTML file</title> - </head> - - <body> - <p>The current version of this document is: &version;</p> - - ¶1; - ¶2; - ¶3; - </body> -</html>]]></programlisting> - </step> - - <step> - <para>Create a new file, <filename>entities.sgml</filename>, with - this content:</para> - - <programlisting><![ CDATA [<!ENTITY version "1.1"> -<!ENTITY para1 SYSTEM "para1.sgml"> -<!ENTITY para2 SYSTEM "para2.sgml"> -<!ENTITY para3 SYSTEM "para3.sgml">]]></programlisting> - </step> - - <step> - <para>Produce <filename>example.html</filename> by normalising - <filename>example.sgml</filename>.</para> - - <screen>&prompt.user; <userinput>sgmlnorm -d example.sgml > example.html</userinput></screen> - </step> - - <step> - <para>Load <filename>example.html</filename> in to your web - browser, and confirm that the - <filename>para<replaceable>n</replaceable>.sgml</filename> files - have been included in <filename>example.html</filename>.</para> - </step> - </procedure> - </sect3> - </sect2> - </sect1> - - <sect1 id="sgml-primer-marked-sections"> - <title>Marked sections</title> - - <para>SGML provides a mechanism to indicate that particular pieces of the - document should be processed in a special way. These are termed - “marked sections”.</para> - - <example> - <title>Structure of a marked section</title> - - <programlisting><![ <replaceable>KEYWORD</replaceable> [ - Contents of marked section -]]></programlisting> - </example> - - <para>As you would expect, being an SGML construct, a marked section - starts with <literal><!</literal>.</para> - - <para>The first square bracket begins to delimit the marked - section.</para> - - <para><replaceable>KEYWORD</replaceable> describes how this marked - section should be processed by the parser.</para> - - <para>The second square bracket indicates that the content of the marked - section starts here.</para> - - <para>The marked section is finished by closing the two square brackets, - and then returning to the document context from the SGML context with - <literal>></literal></para> - - <sect2> - <title>Marked section keywords</title> - - <sect3> - <title><literal>CDATA</literal>, <literal>RCDATA</literal></title> - - <para>These keywords denote the marked sections <emphasis>content - model</emphasis>, and allow you to change it from the - default.</para> - - <para>When an SGML parser is processing a document it keeps track - of what is called the “content model”.</para> - - <para>Briefly, the content model describes what sort of content the - parser is expecting to see, and what it will do with it when it - finds it.</para> - - <para>The two content models you will probably find most useful are - <literal>CDATA</literal> and <literal>RCDATA</literal>.</para> - - <para><literal>CDATA</literal> is for “Character Data”. - If the parser is in this content model then it is expecting to see - characters, and characters only. In this model the < and & - symbols lose their special status, and will be treated as ordinary - characters.</para> - - <para><literal>RCDATA</literal> is for “Entity references and - character data” If the parser is in this content model then it - is expecting to see characters <emphasis>and</emphasis> entities. - < loses its special status, but & will still be treated as - starting the beginning of a general entity.</para> - - <para>This is particularly useful if you are including some verbatim - text that contains lots of < and & characters. While you - could go through the text ensuring that every < is converted to a - &lt; and every & is converted to a &amp;, it can be - easier to mark the section as only containing CDATA. When the SGML - parser encounters this it will ignore the < and & symbols - embedded in the content.</para> - - <!-- The nesting of CDATA within the next example is disgusting --> - - <example> - <title>Using a CDATA marked section</title> - - <programlisting><para>Here is an example of how you would include some text - that contained many &lt; and &amp; symbols. The sample - text is a fragment of HTML. The surrounding text (<para> and - <programlisting>) are from DocBook.</para> - -<programlisting> - <![ CDATA [ <![ CDATA [ - <p>This is a sample that shows you some of the elements within - HTML. Since the angle brackets are used so many times, it's - simpler to say the whole example is a CDATA marked section - than to use the entity names for the left and right angle - brackets throughout.</p> - - <ul> - <li>This is a listitem</li> - <li>This is a second listitem</li> - <li>This is a third listitem</li> - </ul> - - <p>This is the end of the example.</p>]]> - ]]> -</programlisting></programlisting> - - <para>If you look at the source for this document you will see this - technique used throughout.</para> - </example> - </sect3> - - <sect3> - <title><literal>INCLUDE</literal> and - <literal>IGNORE</literal></title> - - <para>If the keyword is <literal>INCLUDE</literal> then the contents - of the marked section will be processed. If the keyword is - <literal>IGNORE</literal> then the marked section is ignored and - will not be processed. It will not appear in the output.</para> - - <example> - <title>Using <literal>INCLUDE</literal> and - <literal>IGNORE</literal> in marked sections</title> - - <programlisting><![ INCLUDE [ - This text will be processed and included. -]]> - -<![ IGNORE [ - This text will not be processed or included. -]]></programlisting> - </example> - - <para>By itself, this isn't too useful. If you wanted to remove text - from your document you could cut it out, or wrap it in - comments.</para> - - <para>It becomes more useful when you realise you can use <link - linkend="sgml-primer-parameter-entities">parameter entities</link> - to control this. Remember that parameter entities can only be used - in SGML contexts, and the keyword of a marked section - <emphasis>is</emphasis> an SGML context.</para> - - <para>For example, suppose that you produced a hard-copy version of - some documentation and an electronic version. In the electronic - version you wanted to include some extra content that wasn't to - appear in the hard-copy.</para> - - <para>Create a parameter entity, and set it's value to - <literal>INCLUDE</literal>. Write your document, using marked - sections to delimit content that should only appear in the - electronic version. In these marked sections use the parameter - entity in place of the keyword.</para> - - <para>When you want to produce the hard-copy version of the document, - change the parameter entity's value to <literal>IGNORE</literal> and - reprocess the document.</para> - - <example> - <title>Using a parameter entity to control a marked - section</title> - - <programlisting><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN" [ -<!ENTITY % electronic.copy "INCLUDE"> -]]> - -... - -<![ %electronic.copy [ - This content should only appear in the electronic - version of the document. -]]></programlisting> - - <para>When producing the hard-copy version, change the entity's - definition to;</para> - - <programlisting><!ENTITY % electronic.copy "IGNORE"></programlisting> - - <para>On reprocessing the document, the marked sections that use - <literal>%electronic.copy</literal> as their keyword will be - ignored.</para> - </example> - </sect3> - </sect2> - - <sect2> - <title>For you to do…</title> - - <procedure> - <step> - <para>Create a new file, <filename>section.sgml</filename>, that - contains the following;</para> - - <programlisting><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN" [ -<!ENTITY % text.output "INCLUDE"> -]> - -<html> - <head> - <title>An example using marked sections</title> - </head> - - <body> - <p>This paragraph <![ CDATA [contains many < - characters (< < < < <) so it is easier - to wrap it in a CDATA marked section ]]></p> - - <![ IGNORE [ - <p>This paragraph will definitely not be included in the - output.</p> - ]]> - - <![ <![ CDATA [%text.output]]> [ - <p>This paragraph might appear in the output, or it - might not.</p> - - <p>Its appearance is controlled by the <![CDATA[%text.output]]> - parameter entity.</p> - ]]> - </body> -</html></programlisting> - </step> - - <step> - <para>Normalise this file using &man.sgmlnorm.1; and examine the - output. Notice which paragraphs have appeared, which have - disappeared, and what has happened to the content of the CDATA - marked section.</para> - </step> - - <step> - <para>Change the definition of the <literal>text.output</literal> - entity from <literal>INCLUDE</literal> to - <literal>IGNORE</literal>. Re-normalise the file, and examine the - output to see what has changed. </para> - </step> - </procedure> - </sect2> - </sect1> - - <sect1> - <title>Conclusion</title> - - <para>That is the conclusion of this SGML primer. For reasons of space - and complexity several things have not been covered in depth (or at - all). However, the previous sections cover enough SGML for you to be - able to follow the organisation of the FDP documentation.</para> - </sect1> -</chapter> - -<!-- - Local Variables: - mode: sgml - sgml-declaration: "../chapter.decl" - sgml-indent-data: t - sgml-omittag: nil - sgml-always-quote-attributes: t - sgml-parent-document: ("../book.sgml" "part" "chapter") - End: ---> |