FreeBSD Documentation Project Primer for New Contributors

The FreeBSD Documentation Project

Thank you for becoming a part of the FreeBSD Documentation Project. Your contribution is extremely valuable.

This primer covers everything you will need to know in order to start contributing to the FreeBSD Documentation Project, from the tools and software you will be using (both mandatory and recommended) to the philosophy behind the Documentation Project.

This document is a work in progress, and is not complete. Sections that are known to be incomplete are indicated with a * in their name.

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.

Important: THIS DOCUMENTATION IS PROVIDED BY THE FREEBSD DOCUMENTATION PROJECT "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 THE FREEBSD DOCUMENTATION PROJECT 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.


Table of Contents
Preface
Shell Prompts
Typographic Conventions
Notes, tips, important information, warnings, and examples
Acknowledgments
1 Overview
1.1 The FreeBSD Documentation Set
1.2 Before you start
1.3 Quick Start
2 Tools
2.1 Mandatory tools
2.1.1 Software
2.1.2 DTDs and Entities
2.1.3 Stylesheets
2.2 Optional tools
2.2.1 Software
3 SGML Primer
3.1 Overview
3.2 Elements, tags, and attributes
3.2.1 For you to do...
3.3 The DOCTYPE declaration
3.3.1 Formal Public Identifiers (FPIs)
3.3.2 Alternatives to FPIs
3.4 Escaping back to SGML
3.5 Comments
3.5.1 For you to do...
3.6 Entities
3.6.1 General Entities
3.6.2 Parameter entities
3.6.3 For you to do...
3.7 Using entities to include files
3.7.1 Using general entities to include files
3.7.2 Using parameter entities to include files
3.7.3 For you to do...
3.8 Marked sections
3.8.1 Marked section keywords
3.8.2 For you to do...
3.9 Conclusion
4 SGML Markup
4.1 HTML
4.1.1 Formal Public Identifier (FPI)
4.1.2 Sectional elements
4.1.3 Block elements
4.1.4 In-line elements
4.1.5 Links
4.2 DocBook
4.2.1 FreeBSD extensions
4.2.2 Formal Public Identifier (FPI)
4.2.3 Document structure
4.2.4 Block elements
4.2.5 In-line elements
4.2.6 Images
4.2.7 Links
5 * Stylesheets
5.1 * DSSSL
5.2 CSS
5.2.1 The Web site (HTML documents)
5.2.2 The DocBook documents
6 Structuring documents under doc/
6.1 The top level, doc/
6.2 The lang.encoding/ directories
6.3 Document specific information
6.3.1 The Handbook
7 The Documentation Build Process
7.1 The FreeBSD Documentation Build Toolset
7.2 Understanding Makefiles in the Documentation tree
7.2.1 Subdirectory Makefiles
7.2.2 Documentation Makefiles
7.3 FreeBSD Documentation Project make includes
7.3.1 doc.project.mk
7.3.2 doc.subdir.mk
8 The Website
8.1 Preparation
8.2 Build the web pages from scratch
8.3 Install the web pages into your web server
8.4 Environment variables
9 Translations
10 Writing style
10.1 Style guide
10.1.1 Letter case
10.1.2 Acronyms
10.1.3 Indentation
10.1.4 Tag style
10.1.5 White space changes
10.1.6 Nonbreaking space
10.2 Word list
11 Using sgml-mode with Emacs
12 See Also
12.1 The FreeBSD Documentation Project
12.2 SGML
12.3 HTML
12.4 DocBook
12.5 The Linux Documentation Project
A. Examples
A.1 DocBook <book>
A.2 DocBook <article>
A.3 Producing formatted output
A.3.1 Using Jade
List of Examples
1. A sample example
3-1. Using an element (start and end tags)
3-2. Using an element (start tag only)
3-3. Elements within elements; <em>
3-4. Using an element with an attribute
3-5. Single quotes around attributes
3-6. .profile, for sh(1) and bash(1) users
3-7. .cshrc, for csh(1) and tcsh(1) users
3-8. SGML generic comment
3-9. Erroneous SGML comments
3-10. Defining general entities
3-11. Defining parameter entities
3-12. Using general entities to include files
3-13. Using parameter entities to include files
3-14. Structure of a marked section
3-15. Using a CDATA marked section
3-16. Using INCLUDE and IGNORE in marked sections
3-17. Using a parameter entity to control a marked section
4-1. Normal HTML document structure
4-2. <h1>, <h2>, etc.
4-3. Bad ordering of <hn> elements
4-4. <p>
4-5. <blockquote>
4-6. <ul> and <ol>
4-7. Definition lists with <dl>
4-8. <pre>
4-9. Simple use of <table>
4-10. Using rowspan
4-11. Using colspan
4-12. Using rowspan and colspan together
4-13. <em> and <strong>
4-14. <b> and <i>
4-15. <tt>
4-16. <big>, <small>, and <font>
4-17. Using <a href="...">
4-18. Using <a name="...">
4-19. Linking to a named part of another document
4-20. Linking to a named part of the same document
4-21. Boilerplate <book> with <bookinfo>
4-22. Boilerplate <article> with <articleinfo>
4-23. A simple chapter
4-24. Empty chapters
4-25. Sections in chapters
4-26. <para>
4-27. <blockquote>
4-28. <warning>
4-29. <itemizedlist>, <orderedlist>, and <procedure>
4-30. <programlisting>
4-31. <co> and <calloutlist>
4-32. <informaltable>
4-33. Tables where frame="none"
4-34. <screen>, <prompt>, and <userinput>
4-35. <emphasis>
4-36. Quotations
4-37. Keys, mouse buttons, and combinations
4-38. Applications, commands, and options.
4-39. <filename>
4-40. <filename> tag with package role
4-41. <devicename>
4-42. <hostid> and roles
4-43. <username>
4-44. <maketarget> and <makevar>
4-45. <literal>
4-46. <replaceable>
4-47. <errorname>
4-48. id on chapters and sections
4-49. <anchor>
4-50. Using <xref>
4-51. Using <link>
4-52. <ulink>
A-1. DocBook <book>
A-2. DocBook <article>
A-3. Converting DocBook to HTML (one large file)
A-4. Converting DocBook to HTML (several small files)
A-5. Converting DocBook to Postscript
A-6. Converting DocBook to PDF

Preface

Shell Prompts

The following table shows the default system prompt and superuser prompt. The examples will use this prompt to indicate which user you should be running the example as.

User Prompt
Normal user %
root #

Typographic Conventions

The following table describes the typographic conventions used in this book.

Meaning Examples
The names of commands. Use ls -l to list all files.
The names of files. Edit your .login file.
On screen computer output.
You have mail.
What you type, when contrasted with on-screen computer output.
% su
Password:
Manual page references. Use su(1) to change user names.
User and group names Only root can do this.
Emphasis You must do this.
Command line variables; replace with the real name or variable. To delete a file, type rm filename
Environment variables $HOME is your home directory.

Notes, tips, important information, warnings, and examples

Within the text appear notes, warnings, and examples.

Note: Notes are represented like this, and contain information that you should take note of, as it may affect what you do.

Tip: Tips are represented like this, and contain information that you might find useful, or lead to an easier way to do something.

Important: Important information is represented like this. Typically they flag extra steps you may need to carry out.

Warning: Warnings are represented like this, and contain information warning you about possible damage if you do not follow the instructions. This damage may be physical, to your hardware or to you, or it may be non-physical, such as the inadvertent deletion of important files.

Example 1. A sample example

Examples are represented like this, and typically contain examples you should walk through, or show you what the results of a particular action should be.


Acknowledgments

My thanks to Sue Blake, Patrick Durusau, Jon Hamilton, Peter Flynn, and Christopher Maden, who took the time to read early drafts of this document and offer many valuable comments and criticisms.


Chapter 1 Overview

Welcome to the FreeBSD Documentation Project. Good quality documentation is very important to the success of FreeBSD, and the FreeBSD Documentation Project (FDP) is how a lot of that documentation is produced. Your contributions are very valuable.

This document's main purpose is to clearly explain how the FDP is organized, how to write and submit documentation to the FDP, and how to effectively use the tools available to you when writing documentation.

Everyone is welcome to join the FDP. There is no minimum membership requirement, no quota of documentation you need to produce per month. All you need to do is subscribe to the FreeBSD documentation project mailing list.

After you have finished reading this document you should:


1.1 The FreeBSD Documentation Set

The FDP is responsible for four categories of FreeBSD documentation.

Manual pages

The English language system manual pages are not written by the FDP, as they are part of the base system. However, the FDP can (and has) re-worded parts of existing manual pages to make them clearer, or to correct inaccuracies.

The translation teams are responsible for translating the system manual pages into different languages. These translations are kept within the FDP.

FAQ

The FAQ aims to address (in short question and answer format) questions that are asked, or should be asked, on the various mailing lists and newsgroups devoted to FreeBSD. The format does not permit long and comprehensive answers.

Handbook

The Handbook aims to be the comprehensive on-line resource and reference for FreeBSD users.

Web site

This is the main FreeBSD presence on the World Wide Web, visible at http://www.FreeBSD.org/ and many mirrors around the world. The web site is many people's first exposure to FreeBSD.

These four groups of documentation are all available in the FreeBSD CVS tree. This means that the logs of changes to these files are visible to anyone, and anyone can use a program such as CVSup or CTM to keep local copies of this documentation.

In addition, many people have written tutorials or other web sites relating to FreeBSD. Some of these are stored in the CVS repository as well (where the author has agreed to this). In other cases the author has decided to keep his documentation separate from the main FreeBSD repository. The FDP endeavors to provide links to as much of this documentation as possible.


1.2 Before you start

This document assumes that you already know:

  • How to maintain an up-to-date local copy of the FreeBSD documentation by maintaining a local copy of the FreeBSD CVS repository (using CVS and either CVSup or CTM) or by using CVSup to download just a checked-out copy.

  • How to download and install new software using either the FreeBSD Ports system or pkg_add(1).


1.3 Quick Start

If you just want to get going, and feel confident you can pick things up as you go along, follow these instructions.

  1. Install the textproc/docproj meta-port.

    # cd /usr/ports/textproc/docproj
    # make JADETEX=no install
    
  2. Get a local copy of the FreeBSD doc tree. Either use CVSup in checkout mode to do this, or get a full copy of the CVS repository locally.

    If you have the CVS repository locally then as a minimum you will need to checkout the doc/share, and doc/en_US.ISO8859-1/share directories.

    % cvs checkout doc/share
    % cvs checkout doc/en_US.ISO8859-1/share
    

    If you have plenty of disk space then you could check out everything.

    % cvs checkout doc
    
  3. If you are preparing a change to an existing book or article, check it out of the repository as necessary. If you are planning on contributing a new book or article then use an existing one as a guide.

    For example, if you want to contribute a new article about setting up a VPN between FreeBSD and Windows 2000 you might do the following.

    1. Check out the articles directory.

      % cvs checkout doc/en_US.ISO8859-1/articles
      
    2. Copy an existing article to use as a template. In this case, you have decided that your new article belongs in a directory called vpn-w2k.

      % cd doc/en_US.ISO8859-1/articles
      % cp -R committers-guide vpn-w2k
      

    If you wanted to edit an existing document, such as the FAQ, which is in doc/en_US.ISO8859-1/books/faq you would check it out of the repository like this.

    % cvs checkout doc/en_US.ISO8859-1/books/faq
    
  4. Edit the .sgml files using your editor of choice.

  5. Test the markup using the lint target. This will quickly find any errors in the document without actually performing the time-consuming transformation.

    % make lint
    

    When you are ready to actually build the document, you may specify a single format or a list of formats in the FORMATS variable. Currently, html, html-split, txt, ps, pdf, and rtf are supported. The most up to date list of supported formats is listed at the top of the doc/share/mk/doc.docbook.mk file. Make sure to use quotes around the list of formats when you build more than one format with a single command.

    For example, to convert the document to html only, you would use:

    % make FORMATS=html
    

    But when you want to convert the document to both html and txt format, you could use either two separate make(1) runs, with:

    % make FORMATS=html
    % make FORMATS=txt
    

    or, you can do it in one command:

    % make FORMATS="html txt"
    
  6. Submit your changes using send-pr(1).


Chapter 2 Tools

The FDP uses a number of different software tools to help manage the FreeBSD documentation, convert it to different output formats, and so on. You will need to use these tools yourself if you are to work with the FreeBSD documentation.

All these tools are available as FreeBSD Ports and Packages, greatly simplifying the work you have to do to install them.

You will need to install these tools before you work through any of the examples in later chapters. The actual usage of these tools is covered in later chapters.

Use textproc/docproj if possible: You can save yourself a lot of time if you install the textproc/docproj port. This is a meta-port which does not contain any software itself. Instead, it depends on various other ports being installed correctly. Installing this port should automatically download and install all of the packages listed in this chapter that you need.

One of the packages that you might need is the JadeTeX macro set. In turn, this macro set requires TeX to be installed. TeX is a large package, and you only need it if you want to produce Postscript or PDF output.

To save yourself time and space you must specify whether or not you want JadeTeX (and therefore TeX) installed when you install this port. Either do:

# make JADETEX=yes install

or

# make JADETEX=no install

as necessary. Alternatively you may install textproc/docproj-jadetex or textproc/docproj-nojadetex. These slave ports define the JADETEX variable for you, therefore they will install the same suite of applications on your machine. Note that you can produce only HTML or ASCII text output if you do not install JadeTeX. PostScript or PDF output require TeX.


2.1 Mandatory tools

2.1.1 Software

These programs are required before you can usefully work with the FreeBSD documentation, and they will allow you to convert the documentation to HTML, plain text, and RTF formats. They are all included in textproc/docproj.

Jade (textproc/jade)

A DSSSL implementation. Used for converting marked up documents to other formats, including HTML and TeX.

Tidy (www/tidy)

An HTML “pretty printer”, used to reformat some of the automatically generated HTML so that it is easier to follow.

Links (www/links)

A text-mode WWW browser that can also convert HTML files to plain text.

peps (graphics/peps)

Some of the documentation includes images, some of which are stored as EPS files. These must be converted to PNG before most web browsers will display them.


2.1.2 DTDs and Entities

These are the DTDs and entity sets used by the FDP. They need to be installed before you can work with any of the documentation.

HTML DTD (textproc/html)

HTML is the markup language of choice for the World Wide Web, and is used throughout the FreeBSD web site.

DocBook DTD (textproc/docbook)

DocBook is designed for marking up technical documentation. All the FreeBSD documentation is written in DocBook.

ISO 8879 entities (textproc/iso8879)

19 of the ISO 8879:1986 character entity sets used by many DTDs. Includes named mathematical symbols, additional characters in the Latin character set (accents, diacriticals, and so on), and Greek symbols.


2.1.3 Stylesheets

The stylesheets are used when converting and formatting the documentation for display on screen, printing, and so on.

Modular DocBook Stylesheets (textproc/dsssl-docbook-modular)

The Modular DocBook Stylesheets are used when converting documentation marked up in DocBook to other formats, such as HTML or RTF.


2.2 Optional tools

You do not need to have any of the following installed. However, you may find it easier to work with the documentation if you do, and they may give you more flexibility in the output formats that can be generated.


2.2.1 Software

JadeTeX and teTeX (print/jadetex and print/teTeX)

Jade and teTeX are used to convert DocBook documents to DVI, Postscript, and PDF formats. The JadeTeX macros are needed in order to do this.

If you do not intend to convert your documentation to one of these formats (i.e., HTML, plain text, and RTF are sufficient) then you do not need to install JadeTeX and teTeX. This can be a significant space and time saver, as teTeX is over 30MB in size.

Important: If you decide to install JadeTeX and teTeX then you will need to configure teTeX after JadeTeX has been installed. print/jadetex/pkg-message contains detailed instructions explaining what you need to do.

Emacs or XEmacs (editors/emacs or editors/xemacs)

Both these editors include a special mode for editing documents marked up according to an SGML DTD. This mode includes commands to reduce the amount of typing you need, and help reduce the possibility of errors.

You do not need to use them; any text editor can be used to edit marked up documents. You may find they make you more efficient.

If anyone has recommendations for other software that is useful when manipulating SGML documents, please let Documentation Engineering Team know, so they can be added to this list.


Chapter 3 SGML Primer

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.

Portions of this section were inspired by Mark Galassi's Get Going With DocBook.


3.1 Overview

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.

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 emphasized, 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.

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.

More precisely, they need help identifying what is what. You or I can look at

To remove /tmp/foo use rm(1).

% rm /tmp/foo
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 cannot. For this we need markup.

“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.

The extra information stored in the markup adds value to the document. Adding the markup to the document must typically be done by a person--after all, if computers could recognize the text sufficiently well to add the markup then there would be no need to add it in the first place. This increases the cost (i.e., the effort required) to create the document.

The previous example is actually represented in this document like this:

<para>To remove <filename>/tmp/foo</filename> use &man.rm.1;.</para>

<screen>&prompt.user; <userinput>rm /tmp/foo</userinput></screen>

As you can see, the markup is clearly separate from the content.

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.

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 meta markup language.

This is exactly what the Standard Generalized Markup Language (SGML) is. Many markup languages have been written in SGML, including the two most used by the FDP, HTML and DocBook.

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 application of SGML.

A DTD is a complete 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 parser 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 “validating the document”.

Note: This processing simply confirms that the choice of elements, their ordering, and so on, conforms to that listed in the DTD. It does not check that you have used appropriate markup for the content. If you tried to 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).

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.


3.2 Elements, tags, and attributes

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 philosophy is that of content and elements.

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.

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.

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.

Notice how you can make this differentiation 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 colors to indicate different chunks of content.

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 tags.

A tag is used to identify where a particular element starts, and where the element ends. The tag is not part of the element itself. Because each DTD was normally written to mark up specific types of information, each one will recognize different elements, and will therefore have different names for the tags.

For an element called element-name the start tag will normally look like <element-name>. The corresponding closing tag for this element is </element-name>.

Example 3-1. Using an element (start and end tags)

HTML has an element for indicating that the content enclosed by the element is a paragraph, called p. This element has both start and end tags.

<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>

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.

Example 3-2. Using an element (start tag only)

HTML has an element for indicating a horizontal rule, called hr. This element does not wrap content, so only has a start tag.

<p>This is a paragraph.</p>

<hr>

<p>This is another paragraph.  A horizontal rule separates this
  from the previous paragraph.</p>

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.

Example 3-3. Elements within elements; <em>

<p>This is a simple <em>paragraph</em> where some
  of the <em>words</em> have been <em>emphasized</em>.</p>

The DTD will specify the rules detailing which elements can contain other elements, and exactly what they can contain.

Important: People often confuse the terms tags and elements, and use the terms as if they were interchangeable. They are not.

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.

When this document (or anyone else knowledgeable about SGML) refers to “the <p> tag” they mean the literal text consisting of the three characters <, p, and >. But the phrase “the <p> element” refers to the whole element.

This distinction is very subtle. But keep it in mind.

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 occurrence of the element, or it might be something else.

An element's attributes are written inside the start tag for that element, and take the form attribute-name="attribute-value".

In sufficiently recent versions of HTML, the <p> element has an attribute called align, which suggests an alignment (justification) for the paragraph to the program displaying the HTML.

The align attribute can take one of four defined values, left, center, right and justify. If the attribute is not specified then the default is left.

Example 3-4. Using an element with an attribute

<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>

Some attributes will only take specific values, such as left or justify. Others will allow you to enter anything you want. If you need to include quotes (") within an attribute then use single quotes around the attribute value.

Example 3-5. Single quotes around attributes

<p align='right'>I am on the right!</p>

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 always quote your attribute values.

The information on attributes, elements, and tags is stored in SGML catalogs. The various Documentation Project tools use these catalog files to validate your work. The tools in textproc/docproj include a variety of SGML catalog files. The FreeBSD Documentation Project includes its own set of catalog files. Your tools need to know about both sorts of catalog files.


3.2.1 For you to do...

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.

  1. Download and install textproc/docproj from the FreeBSD ports system. This is a meta-port that should download and install all of the programs and supporting files that are used by the Documentation Project.

  2. Add lines to your shell startup files to set SGML_CATALOG_FILES. (If you are not working on the English version of the documentation, you will want to substitute the correct directory for your language.)

    Example 3-6. .profile, for sh(1) and bash(1) users

    SGML_ROOT=/usr/local/share/sgml        
    SGML_CATALOG_FILES=${SGML_ROOT}/jade/catalog
    SGML_CATALOG_FILES=${SGML_ROOT}/docbook/4.1/catalog:$SGML_CATALOG_FILES
    SGML_CATALOG_FILES=${SGML_ROOT}/html/catalog:$SGML_CATALOG_FILES
    SGML_CATALOG_FILES=${SGML_ROOT}/iso8879/catalog:$SGML_CATALOG_FILES
    SGML_CATALOG_FILES=/usr/doc/share/sgml/catalog:$SGML_CATALOG_FILES
    SGML_CATALOG_FILES=/usr/doc/en_US.ISO8859-1/share/sgml/catalog:$SGML_CATALOG_FILES
    export SGML_CATALOG_FILES
    

    Example 3-7. .cshrc, for csh(1) and tcsh(1) users

    setenv SGML_ROOT /usr/local/share/sgml
    setenv SGML_CATALOG_FILES ${SGML_ROOT}/jade/catalog
    setenv SGML_CATALOG_FILES ${SGML_ROOT}/docbook/4.1/catalog:$SGML_CATALOG_FILES
    setenv SGML_CATALOG_FILES ${SGML_ROOT}/html/catalog:$SGML_CATALOG_FILES
    setenv SGML_CATALOG_FILES ${SGML_ROOT}/iso8879/catalog:$SGML_CATALOG_FILES
    setenv SGML_CATALOG_FILES /usr/doc/share/sgml/catalog:$SGML_CATALOG_FILES
    setenv SGML_CATALOG_FILES /usr/doc/en_US.ISO8859-1/share/sgml/catalog:$SGML_CATALOG_FILES
    

    Then either log out, and log back in again, or run those commands from the command line to set the variable values.

  1. Create example.sgml, and enter the following text:

    <!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>
    
  2. Try to validate this file using an SGML parser.

    Part of textproc/docproj is the nsgmls validating parser. Normally, nsgmls 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).

    However, when nsgmls is given the -s parameter, nsgmls 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.

    Use nsgmls to check that your document is valid:

    % nsgmls -s example.sgml
    

    As you will see, nsgmls returns without displaying any output. This means that your document validated successfully.

  3. See what happens when required elements are omitted. Try removing the <title> and </title> tags, and re-run the validation.

    % nsgmls -s example.sgml
    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
    

    The error output from nsgmls is organized into colon-separated groups, or columns.

    Column Meaning
    1 The name of the program generating the error. This will always be nsgmls.
    2 The name of the file that contains the error.
    3 Line number where the error appears.
    4 Column number where the error appears.
    5 A one letter code indicating the nature of the message. I indicates an informational message, W is for warnings, and E is for errors[a], and X is for cross-references. As you can see, these messages are errors.
    6 The text of the error message.
    Notes:
    a. It is not always the fifth column either. nsgmls -sv displays nsgmls:I: SP version "1.3" (depending on the installed version). As you can see, this is an informational message.

    Simply omitting the <title> tags has generated 2 different errors.

    The first error indicates that content (in this case, characters, rather than the start tag for an element) has occurred 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 <head> (such as <title>).

    The second error is because <head> elements must contain a <title> element. Because it does not nsgmls 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.

  4. Put the title element back in.


3.3 The DOCTYPE declaration

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.

This information is generally expressed on one line, in the DOCTYPE declaration.

A typical declaration for a document written to conform with version 4.0 of the HTML DTD looks like this:

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN">

That line contains a number of different components.

<!

Is the indicator that indicates that this is an SGML declaration. This line is declaring the document type.

DOCTYPE

Shows that this is an SGML declaration for the document type.

html

Names the first element that will appear in the document.

PUBLIC "-//W3C//DTD HTML 4.0//EN"

Lists the Formal Public Identifier (FPI) for the DTD that this document conforms to. Your SGML parser will use this to find the correct DTD when processing this document.

PUBLIC 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 later.

>

Returns to the document.


3.3.1 Formal Public Identifiers (FPIs)

Note: You do not need to know this, but it is useful background, and might help you debug problems when your SGML processor can not locate the DTD you are using.

FPIs must follow a specific syntax. This syntax is as follows:

"Owner//Keyword Description//Language"
Owner

This indicates the owner of the FPI.

If this string starts with “ISO” then this is an ISO owned FPI. For example, the FPI "ISO 8879:1986//ENTITIES Greek Symbols//EN" lists ISO 8879:1986 as being the owner for the set of entities for Greek symbols. ISO 8879:1986 is the ISO number for the SGML standard.

Otherwise, this string will either look like -//Owner or +//Owner (notice the only difference is the leading + or -).

If the string starts with - then the owner information is unregistered, with a + it identifies it as being registered.

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 organization 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).

Because the FreeBSD Project has not been registered the owner string is -//FreeBSD. And as you can see, the W3C are not a registered owner either.

Keyword

There are several keywords that indicate the type of information in the file. Some of the most common keywords are DTD, ELEMENT, ENTITIES, and TEXT. DTD is used only for DTD files, ELEMENT is usually used for DTD fragments that contain only entity or element declarations. TEXT is used for SGML content (text and tags).

Description

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.

Language

This is an ISO two-character code that identifies the native language for the file. EN is used for English.


3.3.1.1 catalog files

If you use the syntax above 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.

In order to do this it can use a catalog file. A catalog file (typically called catalog) contains lines that map FPIs to filenames. For example, if the catalog file contained the line:

PUBLIC "-//W3C//DTD HTML 4.0//EN"             "4.0/strict.dtd"

The SGML processor would know to look up the DTD from strict.dtd in the 4.0 subdirectory of whichever directory held the catalog file that contained that line.

Look at the contents of /usr/local/share/sgml/html/catalog. This is the catalog file for the HTML DTDs that will have been installed as part of the textproc/docproj port.


3.3.1.2 SGML_CATALOG_FILES

In order to locate a catalog 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.

In addition, you can set SGML_CATALOG_FILES to point to the files. This environment variable should consist of a colon-separated list of catalog files (including their full path).

Typically, you will want to include the following files:

  • /usr/local/share/sgml/docbook/4.1/catalog

  • /usr/local/share/sgml/html/catalog

  • /usr/local/share/sgml/iso8879/catalog

  • /usr/local/share/sgml/jade/catalog

You should already have done this.


3.3.2 Alternatives to FPIs

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.

The syntax for this is slightly different:

<!DOCTYPE html SYSTEM "/path/to/file.dtd">

The SYSTEM 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.

Using FPIs is preferred for reasons of portability. You do not want to have to ship a copy of the DTD around with your document, and if you used the SYSTEM identifier then everyone would need to keep their DTDs in the same place.


3.4 Escaping back to SGML

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.

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.

These sections are marked by <! ... > in your document. Everything between these delimiters is SGML syntax as you might find within a DTD.

As you may just have realized, the DOCTYPE declaration is an example of SGML syntax that you need to include in your document...


3.5 Comments

Comments are an SGML construction, and are normally only valid inside a DTD. However, as Section 3.4 shows, it is possible to use SGML syntax within your document.

The delimiter for SGML comments is the string “--”. The first occurrence of this string opens a comment, and the second closes it.

Example 3-8. SGML generic comment

<!-- test comment -->
<!-- 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 -->

If you have used HTML before you may have been shown different rules for comments. In particular, you may think that the string <!-- opens a comment, and it is only closed by -->.

This is not 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.

Example 3-9. Erroneous SGML comments

<!-- This is in the comment --

     THIS IS OUTSIDE THE COMMENT!

  -- back inside the comment -->

The SGML parser will treat this as though it were actually:

<!THIS IS OUTSIDE THE COMMENT>

This is not valid SGML, and may give confusing error messages.

<!--------------- This is a very bad idea --------------->

As the example suggests, do not write comments like that.

<!--===================================================-->

That is a (slightly) better approach, but it still potentially confusing to people new to SGML.


3.5.1 For you to do...

  1. Add some comments to example.sgml, and check that the file still validates using nsgmls.

  2. Add some invalid comments to example.sgml, and see the error messages that nsgmls gives when it encounters an invalid comment.


3.6 Entities

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.

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.

There are two types of entities which can be used in two different situations; general entities and parameter entities.


3.6.1 General Entities

You cannot use general entities in an SGML context (although you define them in one). They can only be used in your document. Contrast this with parameter entities.

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 &entity-name;. For example, suppose you had an entity called current.version which expanded to the current version number of your product. You could write:

<para>The current version of our product is
  &current.version;.</para>

When the version number changes you can simply change the definition of the value of the general entity and reprocess your document.

You can also use general entities to enter characters that you could not otherwise include in an SGML document. For example, < and & cannot 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.

Fortunately, you can use the two general entities &lt; and &amp; whenever you need to include one or other of these.

A general entity can only be defined within an SGML context. Typically, this is done immediately after the DOCTYPE declaration.

Example 3-10. Defining general entities

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN" [
<!ENTITY current.version    "3.0-RELEASE">
<!ENTITY last.version       "2.2.7-RELEASE">
]>

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.

The square brackets are necessary to indicate that we are extending the DTD indicated by the DOCTYPE declaration.


3.6.2 Parameter entities

Like general entities, 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 SGML context.

Parameter entities are defined in a similar way to general entities. However, instead of using &entity-name; to refer to them, use %entity-name;[1]. The definition also includes the % between the ENTITY keyword and the name of the entity.

Example 3-11. Defining parameter entities

<!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" -->
]>

This may not seem particularly useful. It will be.


3.6.3 For you to do...

  1. Add a general entity to example.sgml.

    <!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>
    
  2. Validate the document using nsgmls.

  3. Load example.sgml into your web browser (you may need to copy it to example.html before your browser recognizes it as an HTML document).

    Unless your browser is very advanced, you will not see the entity reference &version; replaced with the version number. Most web browsers have very simplistic parsers which do not handle proper SGML[2].

  4. The solution is to normalize your document using an SGML normalizer. The normalizer reads in valid SGML and outputs equally valid SGML which has been transformed in some way. One of the ways in which the normalizer transforms the SGML is to expand all the entity references in the document, replacing the entities with the text that they represent.

    You can use sgmlnorm to do this.

    % sgmlnorm example.sgml > example.html
    

    You should find a normalized (i.e., entity references expanded) copy of your document in example.html, ready to load into your web browser.

  5. If you look at the output from sgmlnorm you will see that it does not include a DOCTYPE declaration at the start. To include this you need to use the -d option:

    % sgmlnorm -d example.sgml > example.html
    

3.7 Using entities to include files

Entities (both general and parameter) are particularly useful when used to include one file inside another.


3.7.1 Using general entities to include files

Suppose you have some content for an SGML book organized into files, one file per chapter, called chapter1.sgml, chapter2.sgml, and so forth, with a book.sgml file that will contain these chapters.

In order to use the contents of these files as the values for your entities, you declare them with the SYSTEM keyword. This directs the SGML parser to use the contents of the named file as the value of the entity.

Example 3-12. Using general entities to include files

<!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>

Warning: When using general entities to include other files within a document, the files being included (chapter1.sgml, chapter2.sgml, and so on) must not start with a DOCTYPE declaration. This is a syntax error.


3.7.2 Using parameter entities to include files

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?

You can use this to ensure that you can reuse your general entities.

Suppose that you had many chapters in your document, and you reused these chapters in two different books, each book organizing the chapters in a different fashion.

You could list the entities at the top of each book, but this quickly becomes cumbersome to manage.

Instead, place the general entity definitions inside one file, and use a parameter entity to include that file within your document.

Example 3-13. Using parameter entities to include files

First, place your entity definitions in a separate file, called chapters.ent. This file contains the following:

<!ENTITY chapter.1 SYSTEM "chapter1.sgml">
<!ENTITY chapter.2 SYSTEM "chapter2.sgml">
<!ENTITY chapter.3 SYSTEM "chapter3.sgml">

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:

<!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>

3.7.3 For you to do...

3.7.3.1 Use general entities to include files

  1. Create three files, para1.sgml, para2.sgml, and para3.sgml.

    Put content similar to the following in each file:

    <p>This is the first paragraph.</p>
    
  2. Edit example.sgml so that it looks like this:

    <!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>
    
        &para1;
        &para2;
        &para3;
      </body>
    </html>
    
  3. Produce example.html by normalizing example.sgml.

    % sgmlnorm -d example.sgml > example.html
    
  4. Load example.html into your web browser, and confirm that the paran.sgml files have been included in example.html.


3.7.3.2 Use parameter entities to include files

Note: You must have taken the previous steps first.

  1. Edit example.sgml so that it looks like this:

    <!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>
    
        &para1;
        &para2;
        &para3;
      </body>
    </html>
    
  2. Create a new file, entities.sgml, with this content:

    <!ENTITY version "1.1">
    <!ENTITY para1 SYSTEM "para1.sgml">
    <!ENTITY para2 SYSTEM "para2.sgml">
    <!ENTITY para3 SYSTEM "para3.sgml">
    
  3. Produce example.html by normalizing example.sgml.

    % sgmlnorm -d example.sgml > example.html
    
  4. Load example.html into your web browser, and confirm that the paran.sgml files have been included in example.html.


3.8 Marked sections

SGML provides a mechanism to indicate that particular pieces of the document should be processed in a special way. These are termed “marked sections”.

Example 3-14. Structure of a marked section

<![ KEYWORD [
  Contents of marked section
]]>

As you would expect, being an SGML construct, a marked section starts with <!.

The first square bracket begins to delimit the marked section.

KEYWORD describes how this marked section should be processed by the parser.

The second square bracket indicates that the content of the marked section starts here.

The marked section is finished by closing the two square brackets, and then returning to the document context from the SGML context with >.


3.8.1 Marked section keywords

3.8.1.1 CDATA, RCDATA

These keywords denote the marked sections content model, and allow you to change it from the default.

When an SGML parser is processing a document it keeps track of what is called the “content model”.

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.

The two content models you will probably find most useful are CDATA and RCDATA.

CDATA 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.

RCDATA is for “Entity references and character data” If the parser is in this content model then it is expecting to see characters and entities. < loses its special status, but & will still be treated as starting the beginning of a general entity.

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.

Note: When you use CDATA or RCDATA in examples of text marked up in SGML, keep in mind that the content of CDATA is not validated. You have to check the included SGML text using other means. You could, for example, write the example in another document, validate the example code, and then paste it to your CDATA content.

Example 3-15. Using a CDATA marked section

<para>Here is an example of how you would include some text
  that contained many <literal>&lt;</literal>
  and <literal>&amp;</literal> symbols.  The sample
  text is a fragment of HTML.  The surrounding text (<para> and
  <programlisting>) are from DocBook.</para>

<programlisting>
  <![ 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 is
      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>

If you look at the source for this document you will see this technique used throughout.


3.8.1.2 INCLUDE and IGNORE

If the keyword is INCLUDE then the contents of the marked section will be processed. If the keyword is IGNORE then the marked section is ignored and will not be processed. It will not appear in the output.

Example 3-16. Using INCLUDE and IGNORE in marked sections

<![ INCLUDE [
  This text will be processed and included.
]]>

<![ IGNORE [
  This text will not be processed or included.
]]>

By itself, this is not too useful. If you wanted to remove text from your document you could cut it out, or wrap it in comments.

It becomes more useful when you realize you can use parameter entities to control this. Remember that parameter entities can only be used in SGML contexts, and the keyword of a marked section is an SGML context.

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 was not to appear in the hard-copy.

Create a parameter entity, and set its value to INCLUDE. 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.

When you want to produce the hard-copy version of the document, change the parameter entity's value to IGNORE and reprocess the document.

Example 3-17. Using a parameter entity to control a marked section

<!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.
]]>

When producing the hard-copy version, change the entity's definition to:

<!ENTITY % electronic.copy "IGNORE">

On reprocessing the document, the marked sections that use %electronic.copy as their keyword will be ignored.


3.8.2 For you to do...

  1. Create a new file, section.sgml, that contains the following:

    <!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>
        ]]>
    
        <![ %text.output [
        <p>This paragraph might appear in the output, or it
          might not.</p>
    
        <p>Its appearance is controlled by the %text.output
          parameter entity.</p>      
        ]]>
      </body>
    </html>
    
  2. Normalize this file using 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.

  3. Change the definition of the text.output entity from INCLUDE to IGNORE. Re-normalize the file, and examine the output to see what has changed.


3.9 Conclusion

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 organization of the FDP documentation.


Chapter 4 SGML Markup

This chapter describes the two markup languages you will encounter when you contribute to the FreeBSD documentation project. Each section describes the markup language, and details the markup that you are likely to want to use, or that is already in use.

These markup languages contain a large number of elements, and it can be confusing sometimes to know which element to use for a particular situation. This section goes through the elements you are most likely to need, and gives examples of how you would use them.

This is not an exhaustive list of elements, since that would just reiterate the documentation for each language. The aim of this section is to list those elements more likely to be useful to you. If you have a question about how best to markup a particular piece of content, please post it to the FreeBSD documentation project mailing list.

Inline vs. block: In the remainder of this document, when describing elements, inline means that the element can occur within a block element, and does not cause a line break. A block element, by comparison, will cause a line break (and other processing) when it is encountered.


4.1 HTML

HTML, the HyperText Markup Language, is the markup language of choice on the World Wide Web. More information can be found at <URL:http://www.w3.org/>.

HTML is used to markup pages on the FreeBSD web site. It should not (generally) be used to mark up other documentation, since DocBook offers a far richer set of elements to choose from. Consequently, you will normally only encounter HTML pages if you are writing for the web site.

HTML has gone through a number of versions, 1, 2, 3.0, 3.2, and the latest, 4.0 (available in both strict and loose variants).

The HTML DTDs are available from the ports collection in the textproc/html port. They are automatically installed as part of the textproc/docproj port.


4.1.1 Formal Public Identifier (FPI)

There are a number of HTML FPIs, depending upon the version (also known as the level) of HTML that you want to declare your document to be compliant with.

The majority of HTML documents on the FreeBSD web site comply with the loose version of HTML 4.0.

PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"

4.1.2 Sectional elements

An HTML document is normally split into two sections. The first section, called the head, contains meta-information about the document, such as its title, the name of the author, the parent document, and so on. The second section, the body, contains the content that will be displayed to the user.

These sections are indicated with <head> and <body> elements respectively. These elements are contained within the top-level <html> element.

Example 4-1. Normal HTML document structure

<html>
  <head>
      <title>The document's title</title>
  </head>

  <body>

    ...

  </body>
</html>

4.1.3 Block elements

4.1.3.1 Headings

HTML allows you to denote headings in your document, at up to six different levels.

The largest and most prominent heading is <h1>, then <h2>, continuing down to <h6>.

The element's content is the text of the heading.

Example 4-2. <h1>, <h2>, etc.

Use:

<h1>First section</h1>

<!-- Document introduction goes here -->

<h2>This is the heading for the first section</h2>

<!-- Content for the first section goes here -->

<h3>This is the heading for the first sub-section</h3>

<!-- Content for the first sub-section goes here -->

<h2>This is the heading for the second section</h2>

<!-- Content for the second section goes here -->

Generally, an HTML page should have one first level heading (<h1>). This can contain many second level headings (<h2>), which can in turn contain many third level headings. Each <hn> element should have the same element, but one further up the hierarchy, preceding it. Leaving gaps in the numbering is to be avoided.

Example 4-3. Bad ordering of <hn> elements

Use:

<h1>First section</h1>

<!-- Document introduction -->

<h3>Sub-section</h3>

<!-- This is bad, <h2> has been left out -->

4.1.3.2 Paragraphs

HTML supports a single paragraph element, <p>.

Example 4-4. <p>

Use:

<p>This is a paragraph.  It can contain just about any
  other element.</p>

4.1.3.3 Block quotations

A block quotation is an extended quotation from another document that should not appear within the current paragraph.

Example 4-5. <blockquote>

Use:

<p>A small excerpt from the US Constitution:</p>

<blockquote>We the People of the United States, in Order to form
  a more perfect Union, establish Justice, insure domestic
  Tranquility, provide for the common defence, promote the general
  Welfare, and secure the Blessings of Liberty to ourselves and our
  Posterity, do ordain and establish this Constitution for the
  United States of America.</blockquote>

4.1.3.4 Lists

You can present the user with three types of lists, ordered, unordered, and definition.

Typically, each entry in an ordered list will be numbered, while each entry in an unordered list will be preceded by a bullet point. Definition lists are composed of two sections for each entry. The first section is the term being defined, and the second section is the definition of the term.

Ordered lists are indicated by the <ol> element, unordered lists by the <ul> element, and definition lists by the <dl> element.

Ordered and unordered lists contain listitems, indicated by the <li> element. A listitem can contain textual content, or it may be further wrapped in one or more <p> elements.

Definition lists contain definition terms (<dt>) and definition descriptions (<dd>). A definition term can only contain inline elements. A definition description can contain other block elements.

Example 4-6. <ul> and <ol>

Use:

<p>An unordered list.  Listitems will probably be
  preceded by bullets.</p>

<ul>
  <li>First item</li>

  <li>Second item</li>

  <li>Third item</li>
</ul>

<p>An ordered list, with list items consisting of multiple
  paragraphs.  Each item (note: not each paragraph) will be
  numbered.</p>

<ol>
  <li><p>This is the first item.  It only has one paragraph.</p></li>

  <li><p>This is the first paragraph of the second item.</p>

    <p>This is the second paragraph of the second item.</p></li>

  <li><p>This is the first and only paragraph of the third
    item.</p></li>
</ol>

Example 4-7. Definition lists with <dl>

Use:

<dl>
  <dt>Term 1</dt>

  <dd><p>Paragraph 1 of definition 1.</p>

    <p>Paragraph 2 of definition 1.</p></dd>

  <dt>Term 2</dt>

  <dd><p>Paragraph 1 of definition 2.</p></dd>

  <dt>Term 3</dt>

  <dd><p>Paragraph 1 of definition 3.</p></dd>
</dl>

4.1.3.5 Pre-formatted text

You can indicate that text should be shown to the user exactly as it is in the file. Typically, this means that the text is shown in a fixed font, multiple spaces are not merged into one, and line breaks in the text are significant.

In order to do this, wrap the content in the <pre> element.

Example 4-8. <pre>

You could use <pre> to mark up an email message:

<pre>  From: nik@FreeBSD.org
  To: freebsd-doc@FreeBSD.org
  Subject: New documentation available

  There is a new copy of my primer for contributors to the FreeBSD
  Documentation Project available at

    &lt;URL:http://people.FreeBSD.org/~nik/primer/index.html&gt;

  Comments appreciated.

  N</pre>

Keep in mind that < and & still are recognized as special characters in pre-formatted text. This is why the example shown had to use &lt; instead of <. For consistency, &gt; was used in place of >, too. Watch out for the special characters that may appear in text copied from a plain-text source, e.g., an email message or program code.


4.1.3.6 Tables

Note: Most text-mode browsers (such as Lynx) do not render tables particularly effectively. If you are relying on the tabular display of your content, you should consider using alternative markup to prevent confusion.

Mark up tabular information using the <table> element. A table consists of one or more table rows (<tr>), each containing one or more cells of table data (<td>). Each cell can contain other block elements, such as paragraphs or lists. It can also contain another table (this nesting can repeat indefinitely). If the cell only contains one paragraph then you do not need to include the <p> element.

Example 4-9. Simple use of <table>

Use:

<p>This is a simple 2x2 table.</p>

<table>
  <tr>
    <td>Top left cell</td>

    <td>Top right cell</td>
  </tr>

  <tr>
    <td>Bottom left cell</td>

    <td>Bottom right cell</td>
  </tr>
</table>

A cell can span multiple rows and columns. To indicate this, add the rowspan and/or colspan attributes, with values indicating the number of rows of columns that should be spanned.

Example 4-10. Using rowspan

Use:

<p>One tall thin cell on the left, two short cells next to
  it on the right.</p>

<table>
  <tr>
    <td rowspan="2">Long and thin</td>
  </tr>

  <tr>
    <td>Top cell</td>

    <td>Bottom cell</td>
  </tr>
</table>

Example 4-11. Using colspan

Use:

<p>One long cell on top, two short cells below it.</p>

<table>
  <tr>
    <td colspan="2">Top cell</td>
  </tr>

  <tr>
    <td>Bottom left cell</td>

    <td>Bottom right cell</td>
  </tr>
</table>

Example 4-12. Using rowspan and colspan together

Use:

<p>On a 3x3 grid, the top left block is a 2x2 set of
  cells merged into one.  The other cells are normal.</p>

<table>
  <tr>
    <td colspan="2" rowspan="2">Top left large cell</td>

    <td>Top right cell</td>
  </tr>

  <tr>
    <!-- Because the large cell on the left merges into
         this row, the first <td> will occur on its
         right -->
        
    <td>Middle right cell</td>
  </tr>

  <tr>
    <td>Bottom left cell</td>

    <td>Bottom middle cell</td>

    <td>Bottom right cell</td>
  </tr>
</table>

4.1.4 In-line elements

4.1.4.1 Emphasizing information

You have two levels of emphasis available in HTML, <em> and <strong>. <em> is for a normal level of emphasis and <strong> indicates stronger emphasis.

Typically, <em> is rendered in italic and <strong> is rendered in bold. This is not always the case, however, and you should not rely on it.

Example 4-13. <em> and <strong>

Use:

<p><em>This</em> has been emphasized, while
  <strong>this</strong> has been strongly emphasized.</p>

4.1.4.2 Bold and italics

Because HTML includes presentational markup, you can also indicate that particular content should be rendered in bold or italic. The elements are <b> and <i> respectively.

Example 4-14. <b> and <i>

<p><b>This</b> is in bold, while <i>this</i> is
  in italics.</p>

4.1.4.3 Indicating fixed pitch text

If you have content that should be rendered in a fixed pitch (typewriter) typeface, use <tt> (for “teletype”).

Example 4-15. <tt>

Use:

<p>This document was originally written by
  Nik Clayton, who can be reached by email as
  <tt>nik@FreeBSD.org</tt>.</p>

4.1.4.4 Content size

You can indicate that content should be shown in a larger or smaller font. There are three ways of doing this.

  1. Use <big> and <small> around the content you wish to change size. These tags can be nested, so <big><big>This is much bigger</big></big> is possible.

  2. Use <font> with the size attribute set to +1 or -1 respectively. This has the same effect as using <big> or <small>. However, the use of this approach is deprecated.

  3. Use <font> with the size attribute set to a number between 1 and 7. The default font size is 3. This approach is deprecated.

Example 4-16. <big>, <small>, and <font>

The following fragments all do the same thing.

<p>This text is <small>slightly smaller</small>.  But
  this text is <big>slightly bigger</big>.</p>

<p>This text is <font size="-1">slightly smaller</font>.  But
  this text is <font size="+1">slightly bigger</font.</p>

<p>This text is <font size="2">slightly smaller</font>.  But
  this text is <font size="4">slightly bigger</font>.</p>

4.1.5 Links

Note: Links are also in-line elements.


4.1.5.1 Linking to other documents on the WWW

In order to include a link to another document on the WWW you must know the URL of the document you want to link to.

The link is indicated with <a>, and the href attribute contains the URL of the target document. The content of the element becomes the link, and is normally indicated to the user in some way (underlining, change of color, different mouse cursor when over the link, and so on).

Example 4-17. Using <a href="...">

Use:

<p>More information is available at the
  <a href="http://www.FreeBSD.org/">FreeBSD web site</a>.</p>

These links will take the user to the top of the chosen document.


4.1.5.2 Linking to other parts of documents

Linking to a point within another document (or within the same document) requires that the document author include anchors that you can link to.

Anchors are indicated with <a> and the name attribute instead of href.

Example 4-18. Using <a name="...">

Use:

<p><a name="para1">This</a> paragraph can be referenced
  in other links with the name <tt>para1</tt>.</p>

To link to a named part of a document, write a normal link to that document, but include the name of the anchor after a # symbol.

Example 4-19. Linking to a named part of another document

Assume that the para1 example resides in a document called foo.html.

<p>More information can be found in the
  <a href="foo.html#para1">first paragraph</a> of
  <tt>foo.html</tt>.</p>

If you are linking to a named anchor within the same document then you can omit the document's URL, and just include the name of the anchor (with the preceding #).

Example 4-20. Linking to a named part of the same document

Assume that the para1 example resides in this document:

<p>More information can be found in the
  <a href="#para1">first paragraph</a> of this
  document.</p>

4.2 DocBook

DocBook was originally developed by HaL Computer Systems and O'Reilly & Associates to be a DTD for writing technical documentation [3]. Since 1998 it is maintained by the DocBook Technical Committee. As such, and unlike LinuxDoc and HTML, DocBook is very heavily oriented towards markup that describes what something is, rather than describing how it should be presented.

formal vs. informal: Some elements may exist in two forms, formal and informal. Typically, the formal version of the element will consist of a title followed by the informal version of the element. The informal version will not have a title.

The DocBook DTD is available from the ports collection in the textproc/docbook port. It is automatically installed as part of the textproc/docproj port.


4.2.1 FreeBSD extensions

The FreeBSD Documentation Project has extended the DocBook DTD by adding some new elements. These elements serve to make some of the markup more precise.

Where a FreeBSD specific element is listed below it is clearly marked.

Throughout the rest of this document, the term “DocBook” is used to mean the FreeBSD extended DocBook DTD.

Note: There is nothing about these extensions that is FreeBSD specific, it was just felt that they were useful enhancements for this particular project. Should anyone from any of the other *nix camps (NetBSD, OpenBSD, Linux, ...) be interested in collaborating on a standard DocBook extension set, please get in touch with Documentation Engineering Team .

The FreeBSD extensions are not (currently) in the ports collection. They are stored in the FreeBSD CVS tree, as doc/share/sgml/freebsd.dtd.


4.2.2 Formal Public Identifier (FPI)

In compliance with the DocBook guidelines for writing FPIs for DocBook customizations, the FPI for the FreeBSD extended DocBook DTD is:

PUBLIC "-//FreeBSD//DTD DocBook V4.1-Based Extension//EN"

4.2.3 Document structure

DocBook allows you to structure your documentation in several ways. In the FreeBSD Documentation Project we are using two primary types of DocBook document: the book and the article.

A book is organized into <chapter>s. This is a mandatory requirement. There may be <part>s between the book and the chapter to provide another layer of organization. The Handbook is arranged in this way.

A chapter may (or may not) contain one or more sections. These are indicated with the <sect1> element. If a section contains another section then use the <sect2> element, and so on, up to <sect5>.

Chapters and sections contain the remainder of the content.

An article is simpler than a book, and does not use chapters. Instead, the content of an article is organized into one or more sections, using the same <sect1> (and <sect2> and so on) elements that are used in books.

Obviously, you should consider the nature of the documentation you are writing in order to decide whether it is best marked up as a book or an article. Articles are well suited to information that does not need to be broken down into several chapters, and that is, relatively speaking, quite short, at up to 20-25 pages of content. Books are best suited to information that can be broken up into several chapters, possibly with appendices and similar content as well.

The FreeBSD tutorials are all marked up as articles, while this document, the FreeBSD FAQ, and the FreeBSD Handbook are all marked up as books.


4.2.3.1 Starting a book

The content of the book is contained within the <book> element. As well as containing structural markup, this element can contain elements that include additional information about the book. This is either meta-information, used for reference purposes, or additional content used to produce a title page.

This additional information should be contained within <bookinfo>.

Example 4-21. Boilerplate <book> with <bookinfo>

<book>
  <bookinfo>
    <title>Your title here</title>
    
    <author>
      <firstname>Your first name</firstname>
      <surname>Your surname</surname>
      <affiliation>
        <address><email>Your email address</email></address>
      </affiliation>
    </author>

    <copyright>
      <year>1998</year>
      <holder role="mailto:your email address">Your name</holder>
    </copyright>

    <releaseinfo>$FreeBSD$</releaseinfo>

    <abstract>
      <para>Include an abstract of the book's contents here.</para>
    </abstract>
  </bookinfo>

  ...

</book>

4.2.3.2 Starting an article

The content of the article is contained within the <article> element. As well as containing structural markup, this element can contain elements that include additional information about the article. This is either meta-information, used for reference purposes, or additional content used to produce a title page.

This additional information should be contained within <articleinfo>.

Example 4-22. Boilerplate <article> with <articleinfo>

<article>
  <articleinfo>
    <title>Your title here</title>
    
    <author>
      <firstname>Your first name</firstname>
      <surname>Your surname</surname>
      <affiliation>
        <address><email>Your email address</email></address>
      </affiliation>
    </author>

    <copyright>
      <year>1998</year>
      <holder role="mailto:your email address">Your name</holder>
    </copyright>

    <releaseinfo>$FreeBSD$</releaseinfo>

    <abstract>
      <para>Include an abstract of the article's contents here.</para>
    </abstract>
  </articleinfo>

  ...

</article>

4.2.3.3 Indicating chapters

Use <chapter> to mark up your chapters. Each chapter has a mandatory <title>. Articles do not contain chapters, they are reserved for books.

Example 4-23. A simple chapter

<chapter>
  <title>The chapter's title</title>

  ...
</chapter>

A chapter cannot be empty; it must contain elements in addition to <title>. If you need to include an empty chapter then just use an empty paragraph.

Example 4-24. Empty chapters

<chapter>
  <title>This is an empty chapter</title>

  <para></para>
</chapter>

4.2.3.4 Sections below chapters

In books, chapters may (but do not need to) be broken up into sections, subsections, and so on. In articles, sections are the main structural element, and each article must contain at least one section. Use the <sectn> element. The n indicates the section number, which identifies the section level.

The first <sectn> is <sect1>. You can have one or more of these in a chapter. They can contain one or more <sect2> elements, and so on, down to <sect5>.

Example 4-25. Sections in chapters

<chapter>
  <title>A sample chapter</title>

  <para>Some text in the chapter.</para>

  <sect1>
    <title>First section (1.1)</title>

    ...
  </sect1>

  <sect1>
    <title>Second section (1.2)</title>

    <sect2>
      <title>First sub-section (1.2.1)</title>

      <sect3>
        <title>First sub-sub-section (1.2.1.1)</title>

        ...
      </sect3>
    </sect2>

    <sect2>
      <title>Second sub-section (1.2.2)</title>

      ...
    </sect2>
  </sect1>
</chapter>

Note: This example includes section numbers in the section titles. You should not do this in your documents. Adding the section numbers is carried out by the stylesheets (of which more later), and you do not need to manage them yourself.


4.2.3.5 Subdividing using <part>s

You can introduce another layer of organization between <book> and <chapter> with one or more <part>s. This cannot be done in an <article>.

<part>
  <title>Introduction</title>

  <chapter>
    <title>Overview</title>

    ...
  </chapter>

  <chapter>
    <title>What is FreeBSD?</title>

    ...
  </chapter>

  <chapter>
    <title>History</title>

    ...
  </chapter>
</part>

4.2.4 Block elements

4.2.4.1 Paragraphs

DocBook supports three types of paragraphs: <formalpara>, <para>, and <simpara>.

Most of the time you will only need to use <para>. <formalpara> includes a <title> element, and <simpara> disallows some elements from within <para>. Stick with <para>.

Example 4-26. <para>

Use:

<para>This is a paragraph.  It can contain just about any
  other element.</para>

Appearance:

This is a paragraph. It can contain just about any other element.


4.2.4.2 Block quotations

A block quotation is an extended quotation from another document that should not appear within the current paragraph. You will probably only need it infrequently.

Blockquotes can optionally contain a title and an attribution (or they can be left untitled and unattributed).

Example 4-27. <blockquote>

Use:

<para>A small excerpt from the US Constitution:</para>
          
<blockquote>
  <title>Preamble to the Constitution of the United States</title>

  <attribution>Copied from a web site somewhere</attribution>
        
  <para>We the People of the United States, in Order to form a more perfect
    Union, establish Justice, insure domestic Tranquility, provide for the
    common defence, promote the general Welfare, and secure the Blessings
    of Liberty to ourselves and our Posterity, do ordain and establish this
    Constitution for the United States of America.</para>
</blockquote>

Appearance:

 

Preamble to the Constitution of the United States

We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.

 
--Copied from a web site somewhere  

4.2.4.3 Tips, notes, warnings, cautions, important information and sidebars.

You may need to include extra information separate from the main body of the text. Typically this is “meta” information that the user should be aware of.

Depending on the nature of the information, one of <tip>, <note>, <warning>, <caution>, and <important> should be used. Alternatively, if the information is related to the main text but is not one of the above, use <sidebar>.

The circumstances in which to choose one of these elements over another is unclear. The DocBook documentation suggests:

  • A Note is for information that should be heeded by all readers.

  • An Important element is a variation on Note.

  • A Caution is for information regarding possible data loss or software damage.

  • A Warning is for information regarding possible hardware damage or injury to life or limb.

Example 4-28. <warning>

Use:

<warning>
  <para>Installing FreeBSD may make you want to delete Windows from your
    hard disk.</para>
</warning>

Warning: Installing FreeBSD may make you want to delete Windows from your hard disk.


4.2.4.4 Lists and procedures

You will often need to list pieces of information to the user, or present them with a number of steps that must be carried out in order to accomplish a particular goal.

In order to do this, use <itemizedlist>, <orderedlist>, or <procedure>[4]

<itemizedlist> and <orderedlist> are similar to their counterparts in HTML, <ul> and <ol>. Each one consists of one or more <listitem> elements, and each <listitem> contains one or more block elements. The <listitem> elements are analogous to HTML's <li> tags. However, unlike HTML, they are required.

<procedure> is slightly different. It consists of <step>s, which may in turn consists of more <step>s or <substep>s. Each <step> contains block elements.

Example 4-29. <itemizedlist>, <orderedlist>, and <procedure>

Use:

<itemizedlist>
  <listitem>
    <para>This is the first itemized item.</para>
  </listitem>

  <listitem>
    <para>This is the second itemized item.</para>
  </listitem>
</itemizedlist>

<orderedlist>
  <listitem>
    <para>This is the first ordered item.</para>
  </listitem>

  <listitem>
    <para>This is the second ordered item.</para>
  </listitem>
</orderedlist>

<procedure>
  <step>
    <para>Do this.</para>
  </step>

  <step>
    <para>Then do this.</para>
  </step>

  <step>
    <para>And now do this.</para>
  </step>
</procedure>

Appearance:

  • This is the first itemized item.

  • This is the second itemized item.

  1. This is the first ordered item.

  2. This is the second ordered item.

  1. Do this.

  2. Then do this.

  3. And now do this.


4.2.4.5 Showing file samples

If you want to show a fragment of a file (or perhaps a complete file) to the user, wrap it in the <programlisting> element.

White space and line breaks within <programlisting> are significant. In particular, this means that the opening tag should appear on the same line as the first line of the output, and the closing tag should appear on the same line as the last line of the output, otherwise spurious blank lines may be included.

Example 4-30. <programlisting>

Use:

<para>When you have finished, your program should look like
  this:</para>

<programlisting>#include &lt;stdio.h&gt;

int
main(void)
{
    printf("hello, world\n");
}</programlisting>

Notice how the angle brackets in the #include line need to be referenced by their entities instead of being included literally.

Appearance:

When you have finished, your program should look like this:

#include <stdio.h>

int
main(void)
{
    printf("hello, world\n");
}

4.2.4.6 Callouts

A callout is a mechanism for referring back to an earlier piece of text or specific position within an earlier example without linking to it within the text.

To do this, mark areas of interest in your example (<programlisting>, <literallayout>, or whatever) with the <co> element. Each element must have a unique id assigned to it. After the example include a <calloutlist> that refers back to the example and provides additional commentary.

Example 4-31. <co> and <calloutlist>

<para>When you have finished, your program should look like
  this:</para>

<programlisting>#include &lt;stdio.h&gt; <co id="co-ex-include">

int <co id="co-ex-return">
main(void)
{
    printf("hello, world\n"); <co id="co-ex-printf">
}</programlisting>

<calloutlist>
  <callout arearefs="co-ex-include">
    <para>Includes the standard IO header file.</para>
  </callout>

  <callout arearefs="co-ex-return">
    <para>Specifies that <function>main()</function> returns an
      int.</para>
  </callout>

  <callout arearefs="co-ex-printf">
    <para>The <function>printf()</function> call that writes
      <literal>hello, world</literal> to standard output.</para>
  </callout>
</calloutlist>

Appearance:

When you have finished, your program should look like this:

#include <stdio.h> (1)

int (2)
main(void)
{
    printf("hello, world\n"); (3)
}
(1)
Includes the standard IO header file.
(2)
Specifies that main() returns an int.
(3)
The printf() call that writes hello, world to standard output.

4.2.4.7 Tables

Unlike HTML, you do not need to use tables for layout purposes, as the stylesheet handles those issues for you. Instead, just use tables for marking up tabular data.

In general terms (and see the DocBook documentation for more detail) a table (which can be either formal or informal) consists of a <table> element. This contains at least one <tgroup> element, which specifies (as an attribute) the number of columns in this table group. Within the tablegroup you can then have one <thead> element, which contains elements for the table headings (column headings), and one <tbody> which contains the body of the table.

Both <tgroup> and <thead> contain <row> elements, which in turn contain <entry> elements. Each <entry> element specifies one cell in the table.

Example 4-32. <informaltable>

Use:

<informaltable frame="none" pgwide="1">
  <tgroup cols="2">
    <thead>
      <row>
        <entry>This is column head 1</entry>
        <entry>This is column head 2</entry>
      </row>
    </thead>

    <tbody>
      <row>
        <entry>Row 1, column 1</entry>
        <entry>Row 1, column 2</entry>
      </row>

      <row>
        <entry>Row 2, column 1</entry>
        <entry>Row 2, column 2</entry>
      </row>
    </tbody>
  </tgroup>
</informaltable>

Appearance:

This is column head 1 This is column head 2
Row 1, column 1 Row 1, column 2
Row 2, column 1 Row 2, column 2

Always use the pgwide attribute with a value of 1 with the <informaltable> element. A bug in Internet Explorer can cause the table to render incorrectly if this is omitted.

If you do not want a border around the table the frame attribute can be added to the <informaltable> element with a value of none (i.e., <informaltable frame="none">).

Example 4-33. Tables where frame="none"

Appearance:

This is column head 1 This is column head 2
Row 1, column 1 Row 1, column 2
Row 2, column 1 Row 2, column 2

4.2.4.8 Examples for the user to follow

A lot of the time you need to show examples for the user to follow. Typically, these will consist of dialogs with the computer; the user types in a command, the user gets a response back, they type in another command, and so on.

A number of distinct elements and entities come into play here.

<screen>

Everything the user sees in this example will be on the computer screen, so the next element is <screen>.

Within <screen>, white space is significant.

<prompt>, &prompt.root; and &prompt.user;

Some of the things the user will be seeing on the screen are prompts from the computer (either from the operating system, command shell, or application). These should be marked up using <prompt>.

As a special case, the two shell prompts for the normal user and the root user have been provided as entities. Every time you want to indicate the user is at a shell prompt, use one of &prompt.root; and &prompt.user; as necessary. They do not need to be inside <prompt>.

Note: &prompt.root; and &prompt.user; are FreeBSD extensions to DocBook, and are not part of the original DTD.

<userinput>

When displaying text that the user should type in, wrap it in <userinput> tags. It will probably be displayed differently to the user.

Example 4-34. <screen>, <prompt>, and <userinput>

Use:

<screen>&prompt.user; <userinput>ls -1</userinput>
foo1
foo2
foo3
&prompt.user; <userinput>ls -1 | grep foo2</userinput>
foo2
&prompt.user; <userinput>su</userinput>
<prompt>Password: </prompt>
&prompt.root; <userinput>cat foo2</userinput>
This is the file called 'foo2'</screen>

Appearance:

% ls -1
foo1
foo2
foo3
% ls -1 | grep foo2
foo2
% su
Password: 
# cat foo2
This is the file called 'foo2'

Note: Even though we are displaying the contents of the file foo2, it is not marked up as <programlisting>. Reserve <programlisting> for showing fragments of files outside the context of user actions.


4.2.5 In-line elements

4.2.5.1 Emphasizing information

When you want to emphasize a particular word or phrase, use <emphasis>. This may be presented as italic, or bold, or might be spoken differently with a text-to-speech system.

There is no way to change the presentation of the emphasis within your document, no equivalent of HTML's <b> and <i>. If the information you are presenting is important then consider presenting it in <important> rather than <emphasis>.

Example 4-35. <emphasis>

Use:

<para>FreeBSD is without doubt <emphasis>the</emphasis>
  premiere Unix like operating system for the Intel architecture.</para>

Appearance:

FreeBSD is without doubt the premiere Unix like operating system for the Intel architecture.


4.2.5.2 Quotations

To quote text from another document or source, or to denote a phrase that is used figuratively, use <quote>. Within a <quote> tag, you may use most of the markup tags available for normal text.

Example 4-36. Quotations

Use:

<para>However, make sure that the search does not go beyond the
  <quote>boundary between local and public administration</quote>,
  as RFC 1535 calls it.</para>

Appearance:

However, make sure that the search does not go beyond the “boundary between local and public administration”, as RFC 1535 calls it.


4.2.5.3 Keys, mouse buttons, and combinations

To refer to a specific key on the keyboard, use <keycap>. To refer to a mouse button, use <mousebutton>. And to refer to combinations of key presses or mouse clicks, wrap them all in <keycombo>.

<keycombo> has an attribute called action, which may be one of click, double-click, other, press, seq, or simul. The last two values denote whether the keys or buttons should be pressed in sequence, or simultaneously.

The stylesheets automatically add any connecting symbols, such as +, between the key names, when wrapped in <keycombo>.

Example 4-37. Keys, mouse buttons, and combinations

Use:

<para>To switch to the second virtual terminal, press 
  <keycombo action="simul"><keycap>Alt</keycap>
    <keycap>F1</keycap></keycombo>.</para>

<para>To exit <command>vi</command> without saving your work, type
  <keycombo action="seq"><keycap>Esc</keycap><keycap>:</keycap>
    <keycap>q</keycap><keycap>!</keycap></keycombo>.</para>

<para>My window manager is configured so that
  <keycombo action="simul"><keycap>Alt</keycap>
    <mousebutton>right</mousebutton>
  </keycombo> mouse button is used to move windows.</para>

Appearance:

To switch to the second virtual terminal, press Alt+F1.

To exit vi without saving your work, type Esc : q !.

My window manager is configured so that Alt+right mouse button is used to move windows.


4.2.5.4 Applications, commands, options, and cites

You will frequently want to refer to both applications and commands when writing for the Handbook. The distinction between them is simple: an application is the name for a suite (or possibly just 1) of programs that fulfil a particular task. A command is the name of a program that the user can run.

In addition, you will occasionally need to list one or more of the options that a command might take.

Finally, you will often want to list a command with its manual section number, in the “command(number)” format so common in Unix manuals.

Mark up application names with <application>.

When you want to list a command with its manual section number (which should be most of the time) the DocBook element is <citerefentry>. This will contain a further two elements, <refentrytitle> and <manvolnum>. The content of <refentrytitle> is the name of the command, and the content of <manvolnum> is the manual page section.

This can be cumbersome to write, and so a series of general entities have been created to make this easier. Each entity takes the form &man.manual-page.manual-section;.

The file that contains these entities is in doc/share/sgml/man-refs.ent, and can be referred to using this FPI:

PUBLIC "-//FreeBSD//ENTITIES DocBook Manual Page Entities//EN"

Therefore, the introduction to your documentation will probably look like this:

<!DOCTYPE book PUBLIC "-//FreeBSD//DTD DocBook V4.1-Based Extension//EN" [

<!ENTITY % man PUBLIC "-//FreeBSD//ENTITIES DocBook Manual Page Entities//EN">
%man;

...

]>

Use <command> when you want to include a command name “in-line” but present it as something the user should type in.

Use <option> to mark up the options which will be passed to a command.

When referring to the same command multiple times in close proximity it is preferred to use the &man.command.section; notation to markup the first reference and use <command> to markup subsequent references. This makes the generated output, especially HTML, appear visually better.

This can be confusing, and sometimes the choice is not always clear. Hopefully this example makes it clearer.

Example 4-38. Applications, commands, and options.

Use:

<para><application>Sendmail</application> is the most
  widely used Unix mail application.</para>

<para><application>Sendmail</application> includes the
  <citerefentry>
    <refentrytitle>sendmail</refentrytitle>
    <manvolnum>8</manvolnum>
  </citerefentry>, &man.mailq.8;, and &man.newaliases.8;
  programs.</para>

<para>One of the command line parameters to <citerefentry>
    <refentrytitle>sendmail</refentrytitle>
    <manvolnum>8</manvolnum>
  </citerefentry>, <option>-bp</option>, will display the current
  status of messages in the mail queue.  Check this on the command
  line by running <command>sendmail -bp</command>.</para>

Appearance:

Sendmail is the most widely used Unix mail application.

Sendmail includes the sendmail(8), mailq(8), and newaliases(8) programs.

One of the command line parameters to sendmail(8), -bp, will display the current status of messages in the mail queue. Check this on the command line by running sendmail -bp.

Note: Notice how the &man.command.section; notation is easier to follow.


4.2.5.5 Files, directories, extensions

Whenever you wish to refer to the name of a file, a directory, or a file extension, use <filename>.

Example 4-39. <filename>

Use:

<para>The SGML source for the Handbook in English can be
  found in <filename class="directory">/usr/doc/en/handbook/</filename>.  The first
  file is called <filename>handbook.sgml</filename> in that
  directory.  You should also see a <filename>Makefile</filename>
  and a number of files with a <filename>.ent</filename>
  extension.</para>

Appearance:

The SGML source for the Handbook in English can be found in /usr/doc/en/handbook/. The first file is called handbook.sgml in that directory. You should also see a Makefile and a number of files with a .ent extension.


4.2.5.6 The name of ports

FreeBSD extension: These elements are part of the FreeBSD extension to DocBook, and do not exist in the original DocBook DTD.

You might need to include the name of a program from the FreeBSD Ports Collection in the documentation. Use the <filename> tag with the role attribute set to package to identify these. Since ports can be installed in any number of locations, only include the category and the port name; do not include /usr/ports.

Example 4-40. <filename> tag with package role

Use:

<para>Install the <filename role="package">net/ethereal</filename> port to view network traffic.</para>

Appearance:

Install the net/ethereal port to view network traffic.


4.2.5.7 Devices

FreeBSD extension: These elements are part of the FreeBSD extension to DocBook, and do not exist in the original DocBook DTD.

When referring to devices you have two choices. You can either refer to the device as it appears in /dev, or you can use the name of the device as it appears in the kernel. For this latter course, use <devicename>.

Sometimes you will not have a choice. Some devices, such as networking cards, do not have entries in /dev, or the entries are markedly different from those entries.

Example 4-41. <devicename>

Use:

<para><devicename>sio</devicename> is used for serial
  communication in FreeBSD.  <devicename>sio</devicename> manifests
  through a number of entries in <filename>/dev</filename>, including
  <filename>/dev/ttyd0</filename> and <filename>/dev/cuaa0</filename>.</para>

<para>By contrast, the networking devices, such as
  <devicename>ed0</devicename> do not appear in <filename>/dev</filename>.</para>

<para>In MS-DOS, the first floppy drive is referred to as
  <devicename>a:</devicename>.  In FreeBSD it is
  <filename>/dev/fd0</filename>.</para>

Appearance:

sio is used for serial communication in FreeBSD. sio manifests through a number of entries in /dev, including /dev/ttyd0 and /dev/cuaa0.

By contrast, the networking devices, such as ed0 do not appear in /dev.

In MS-DOS, the first floppy drive is referred to as a:. In FreeBSD it is /dev/fd0.


4.2.5.8 Hosts, domains, IP addresses, and so forth

FreeBSD extension: These elements are part of the FreeBSD extension to DocBook, and do not exist in the original DocBook DTD.

You can markup identification information for networked computers (hosts) in several ways, depending on the nature of the information. All of them use <hostid> as the element, with the role attribute selecting the type of the marked up information.

No role attribute, or role="hostname"

With no role attribute (i.e., <hostid>...</hostid>) the marked up information is the simple hostname, such as freefall or wcarchive. You can explicitly specify this with role="hostname".

role="domainname"

The text is a domain name, such as FreeBSD.org or ngo.org.uk. There is no hostname component.

role="fqdn"

The text is a Fully Qualified Domain Name, with both hostname and domain name parts.

role="ipaddr"

The text is an IP address, probably expressed as a dotted quad.

role="ip6addr"

The text is an IPv6 address.

role="netmask"

The text is a network mask, which might be expressed as a dotted quad, a hexadecimal string, or as a / followed by a number.

role="mac"

The text is an Ethernet MAC address, expressed as a series of 2 digit hexadecimal numbers separated by colons.

Example 4-42. <hostid> and roles

Use:

<para>The local machine can always be referred to by the
  name <hostid>localhost</hostid>, which will have the IP address
  <hostid role="ipaddr">127.0.0.1</hostid>.</para>

<para>The <hostid role="domainname">FreeBSD.org</hostid> domain
  contains a number of different hosts, including
  <hostid role="fqdn">freefall.FreeBSD.org</hostid> and
  <hostid role="fqdn">bento.FreeBSD.org</hostid>.</para>

<para>When adding an IP alias to an interface (using
  <command>ifconfig</command>) <emphasis>always</emphasis> use a
  netmask of <hostid role="netmask">255.255.255.255</hostid>
  (which can also be expressed as <hostid
    role="netmask">0xffffffff</hostid>.</para>

<para>The MAC address uniquely identifies every network card
  in existence.  A typical MAC address looks like <hostid
    role="mac">08:00:20:87:ef:d0</hostid>.</para>

Appearance:

The local machine can always be referred to by the name localhost, which will have the IP address 127.0.0.1.

The FreeBSD.org domain contains a number of different hosts, including freefall.FreeBSD.org and bento.FreeBSD.org.

When adding an IP alias to an interface (using ifconfig) always use a netmask of 255.255.255.255 (which can also be expressed as 0xffffffff.

The MAC address uniquely identifies every network card in existence. A typical MAC address looks like 08:00:20:87:ef:d0.


4.2.5.9 Usernames

FreeBSD extension: These elements are part of the FreeBSD extension to DocBook, and do not exist in the original DocBook DTD.

When you need to refer to a specific username, such as root or bin, use <username>.

Example 4-43. <username>

Use:

<para>To carry out most system administration functions you
  will need to be <username>root</username>.</para>

Appearance:

To carry out most system administration functions you will need to be root.


4.2.5.10 Describing Makefiles

FreeBSD extension: These elements are part of the FreeBSD extension to DocBook, and do not exist in the original DocBook DTD.

Two elements exist to describe parts of Makefiles, <maketarget> and <makevar>.

<maketarget> identifies a build target exported by a Makefile that can be given as a parameter to make. <makevar> identifies a variable that can be set (in the environment, on the make command line, or within the Makefile) to influence the process.

Example 4-44. <maketarget> and <makevar>

Use:

<para>Two common targets in a <filename>Makefile</filename>
  are <maketarget>all</maketarget> and <maketarget>clean</maketarget>.</para>

<para>Typically, invoking <maketarget>all</maketarget> will rebuild the
  application, and invoking <maketarget>clean</maketarget> will remove
  the temporary files (<filename>.o</filename> for example) created by
  the build process.</para>

<para><maketarget>clean</maketarget> may be controlled by a number of
  variables, including <makevar>CLOBBER</makevar> and
  <makevar>RECURSE</makevar>.</para>

Appearance:

Two common targets in a Makefile are all and clean.

Typically, invoking all will rebuild the application, and invoking clean will remove the temporary files (.o for example) created by the build process.

clean may be controlled by a number of variables, including CLOBBER and RECURSE.


4.2.5.11 Literal text

You will often need to include “literal” text in the Handbook. This is text that is excerpted from another file, or which should be copied from the Handbook into another file verbatim.

Some of the time, <programlisting> will be sufficient to denote this text. <programlisting> is not always appropriate, particularly when you want to include a portion of a file “in-line” with the rest of the paragraph.

On these occasions, use <literal>.

Example 4-45. <literal>

Use:

<para>The <literal>maxusers 10</literal> line in the kernel
  configuration file determines the size of many system tables, and is
  a rough guide to how many simultaneous logins the system will
  support.</para>

Appearance:

The maxusers 10 line in the kernel configuration file determines the size of many system tables, and is a rough guide to how many simultaneous logins the system will support.


4.2.5.12 Showing items that the user must fill in

There will often be times when you want to show the user what to do, or refer to a file, or command line, or similar, where the user cannot simply copy the examples that you provide, but must instead include some information themselves.

<replaceable> is designed for this eventuality. Use it inside other elements to indicate parts of that element's content that the user must replace.

Example 4-46. <replaceable>

Use:

<informalexample>
  <screen>&prompt.user; <userinput>man <replaceable>command</replaceable></userinput></screen>
</informalexample>

Appearance:

% man command

<replaceable> can be used in many different elements, including <literal>. This example also shows that <replaceable> should only be wrapped around the content that the user is meant to provide. The other content should be left alone.

Use:

<para>The <literal>maxusers <replaceable>n</replaceable></literal>
  line in the kernel configuration file determines the size of many system
  tables, and is a rough guide to how many simultaneous logins the system will
  support.</para>

<para>For a desktop workstation, <literal>32</literal> is a good value
  for <replaceable>n</replaceable>.</para>

Appearance:

The maxusers n line in the kernel configuration file determines the size of many system tables, and is a rough guide to how many simultaneous logins the system will support.

For a desktop workstation, 32 is a good value for n.


4.2.5.13 Quoting system errors

You might want to show errors generated by FreeBSD. Mark these with <errorname>. This indicates the exact error that appears.

Example 4-47. <errorname>

Use:

 
<screen><errorname>Panic: cannot mount root</errorname></screen>

Appearance:

Panic: cannot mount root

4.2.6 Images

Important: Image support in the documentation is currently extremely experimental. I think the mechanisms described here are unlikely to change, but that is not guaranteed.

You will also need to install the graphics/ImageMagick port, which is used to convert between the different image formats. This is a big port, and most of it is not required. However, while we are working on the Makefiles and other infrastructure it makes things easier. This port is not in the textproc/docproj meta port, you must install it by hand.

The best example of what follows in practice is the doc/en_US.ISO8859-1/articles/vm-design/ document. If you are unsure of the description that follows, take a look at the files in that directory to see how everything hangs together. Experiment with creating different formatted versions of the document to see how the image markup appears in the formatted output.


4.2.6.1 Image formats

We currently support two formats for images. The format you should use will depend on the nature of your image.

For images that are primarily vector based, such as network diagrams, time lines, and similar, use Encapsulated Postscript, and make sure that your images have the .eps extension.

For bitmaps, such as screen captures, use the Portable Network Graphic format, and make sure that your images have the .png extension.

These are the only formats in which images should be committed to the CVS repository.

Use the right format for the right image. It is to be expected that your documentation will have a mix of EPS and PNG images. The Makefiles ensure that the correct format image is chosen depending on the output format that you use for your documentation. Do not commit the same image to the repository in two different formats.

Important: It is anticipated that the Documentation Project will switch to using the Scalable Vector Graphic (SVG) format for vector images. However, the current state of SVG capable editing tools makes this impractical.


4.2.6.2 Markup

The markup for an image is relatively simple. First, markup a <mediaobject>. The <mediaobject> can contain other, more specific objects. We are concerned with two, the <imageobject> and the <textobject>.

You should include one <imageobject>, and two <textobject> elements. The <imageobject> will point to the name of the image file that will be used (without the extension). The <textobject> elements contain information that will be presented to the user as well as, or instead of, the image.

There are two circumstances where this can happen.

  • When the reader is viewing the documentation in HTML. In this case, each image will need to have associated alternate text to show the user, typically whilst the image is loading, or if they hover the mouse pointer over the image.

  • When the reader is viewing the documentation in plain text. In this case, each image should have an ASCII art equivalent to show the user.

An example will probably make things easier to understand. Suppose you have an image, called fig1, that you want to include in the document. This image is of a rectangle with an A inside it. The markup for this would be as follows.

<mediaobject>
  <imageobject>
    <imagedata fileref="fig1"> (1)
  </imageobject>

  <textobject>
    <literallayout class="monospaced">+---------------+ (2)
|       A       |
+---------------+</literallayout>
  </textobject>

  <textobject>
    <phrase>A picture</phrase> (3)
  </textobject>
</mediaobject>
(1)
Include an <imagedata> element inside the <imageobject> element. The fileref attribute should contain the filename of the image to include, without the extension. The stylesheets will work out which extension should be added to the filename automatically.
(2)
The first <textobject> should contain a <literallayout> element, where the class attribute is set to monospaced. This is your opportunity to demonstrate your ASCII art skills. This content will be used if the document is converted to plain text.

Notice how the first and last lines of the content of the <literallayout> element butt up next to the element's tags. This ensures no extraneous white space is included.

(3)
The second <textobject> should contain a single <phrase> element. The contents of this will become the alt attribute for the image when this document is converted to HTML.

4.2.6.3 Makefile entries

Your images must be listed in the Makefile in the IMAGES variable. This variable should contain the name of all your source images. For example, if you have created three figures, fig1.eps, fig2.png, fig3.png, then your Makefile should have lines like this in it.

...
IMAGES= fig1.eps fig2.png fig3.png
...

or

...
IMAGES=  fig1.eps
IMAGES+= fig2.png
IMAGES+= fig3.png
...

Again, the Makefile will work out the complete list of images it needs to build your source document, you only need to list the image files you provided.


4.2.6.4 Images and chapters in subdirectories

You must be careful when you separate your documentation into smaller files (see Section 3.7.1) in different directories.

Suppose you have a book with three chapters, and the chapters are stored in their own directories, called chapter1/chapter.sgml, chapter2/chapter.sgml, and chapter3/chapter.sgml. If each chapter has images associated with it, I suggest you place those images in each chapter's subdirectory (chapter1/, chapter2/, and chapter3/).

However, if you do this you must include the directory names in the IMAGES variable in the Makefile, and you must include the directory name in the <imagedata> element in your document.

For example, if you have chapter1/fig1.png, then chapter1/chapter.sgml should contain:

<mediaobject>
  <imageobject>
    <imagedata fileref="chapter1/fig1"> (1)
  </imageobject>

  ...

</mediaobject>
(1)
The directory name must be included in the fileref attribute.

The Makefile must contain:

...
IMAGES=  chapter1/fig1.png
...

Then everything should just work.


4.2.7 Links

Note: Links are also in-line elements.


4.2.7.1 Linking to other parts of the same document

Linking within the same document requires you to specify where you are linking from (i.e., the text the user will click, or otherwise indicate, as the source of the link) and where you are linking to (the link's destination).

Each element within DocBook has an attribute called id. You can place text in this attribute to uniquely name the element it is attached to.

This value will be used when you specify the link source.

Normally, you will only be linking to chapters or sections, so you would add the id attribute to these elements.

Example 4-48. id on chapters and sections

<chapter id="chapter1">
  <title>Introduction</title>

  <para>This is the introduction.  It contains a subsection,
    which is identified as well.</para>

  <sect1 id="chapter1-sect1">
    <title>Sub-sect 1</title>

    <para>This is the subsection.</para>
  </sect1>
</chapter>

Obviously, you should use more descriptive values. The values must be unique within the document (i.e., not just the file, but the document the file might be included in as well). Notice how the id for the subsection is constructed by appending text to the id of the chapter. This helps to ensure that they are unique.

If you want to allow the user to jump into a specific portion of the document (possibly in the middle of a paragraph or an example), use <anchor>. This element has no content, but takes an id attribute.

Example 4-49. <anchor>

<para>This paragraph has an embedded
  <anchor id="para1">link target in it.  It will not show up in
  the document.</para>

When you want to provide the user with a link they can activate (probably by clicking) to go to a section of the document that has an id attribute, you can use either <xref> or <link>.

Both of these elements have a linkend attribute. The value of this attribute should be the value that you have used in a id attribute (it does not matter if that value has not yet occurred in your document; this will work for forward links as well as backward links).

If you use <xref> then you have no control over the text of the link. It will be generated for you.

Example 4-50. Using <xref>

Assume that this fragment appears somewhere in a document that includes the id example:

<para>More information can be found
  in <xref linkend="chapter1">.</para>

<para>More specific information can be found
  in <xref linkend="chapter1-sect1">.</para>

The text of the link will be generated automatically, and will look like (emphasized text indicates the text that will be the link):

More information can be found in Chapter One.

More specific information can be found in the section called Sub-sect 1.

Notice how the text from the link is derived from the section title or the chapter number.

Note: This means that you cannot use <xref> to link to an id attribute on an <anchor> element. The <anchor> has no content, so the <xref> cannot generate the text for the link.

If you want to control the text of the link then use <link>. This element wraps content, and the content will be used for the link.

Example 4-51. Using <link>

Assume that this fragment appears somewhere in a document that includes the id example.

<para>More information can be found in
  <link linkend="chapter1">the first chapter</link>.</para>

<para>More specific information can be found in
  <link linkend="chapter1-sect1">this</link> section.</para>

This will generate the following (emphasized text indicates the text that will be the link):

More information can be found in the first chapter.

More specific information can be found in this section.

Note: That last one is a bad example. Never use words like “this” or “here” as the source for the link. The reader will need to hunt around the surrounding context to see where the link is actually taking them.

Note: You can use <link> to include a link to an id on an <anchor> element, since the <link> content defines the text that will be used for the link.


4.2.7.2 Linking to documents on the WWW

Linking to external documents is much simpler, as long as you know the URL of the document you want to link to. Use <ulink>. The url attribute is the URL of the page that the link points to, and the content of the element is the text that will be displayed for the user to activate.

Example 4-52. <ulink>

Use:

<para>Of course, you could stop reading this document and
  go to the <ulink url="&url.base;/index.html">FreeBSD
  home page</ulink> instead.</para>

Appearance:

Of course, you could stop reading this document and go to the FreeBSD home page instead.


Chapter 5 * Stylesheets

SGML says nothing about how a document should be displayed to the user, or rendered on paper. To do that, various languages have been developed to describe stylesheets, including DynaText, Panorama, SPICE, JSSS, FOSI, CSS, and DSSSL.

For DocBook, we are using stylesheets written in DSSSL. For HTML we are using CSS.


5.1 * DSSSL

The Documentation Project uses a slightly customized version of Norm Walsh's modular DocBook stylesheets.

These can be found in textproc/dsssl-docbook-modular.

The modified stylesheets are not in the ports system. Instead they are part of the Documentation Project source repository, and can be found in doc/share/sgml/freebsd.dsl. It is well commented, and pending completion of this section you are encouraged to examine that file to see how some of the available options in the standard stylesheets have been configured in order to customize the output for the FreeBSD Documentation Project. That file also contains examples showing how to extend the elements that the stylesheet understands, which is how the FreeBSD specific elements have been formatted.


5.2 CSS

Cascading Stylesheets (CSS) are a mechanism for attaching style information (font, weight, size, color, and so forth) to elements in an HTML document without abusing HTML to do so.


5.2.1 The Web site (HTML documents)

The FreeBSD web site does not currently use CSS. Unfortunately, the look and feel is constructed using abuses of HTML of varying degrees. This should be fixed, and would be a good project for someone looking to contribute to the documentation project.


5.2.2 The DocBook documents

The FreeBSD DSSSL stylesheets include a reference to a stylesheet, docbook.css, which is expected to appear in the same directory as the HTML files. The project-wide CSS file is copied from doc/share/misc/docbook.css when documents are converted to HTML, and is installed automatically.


Chapter 6 Structuring documents under doc/

The doc/ tree is organized in a particular fashion, and the documents that are part of the FDP are in turn organized in a particular fashion. The aim is to make it simple to add new documentation into the tree and:

  1. make it easy to automate converting the document to other formats;

  2. promote consistency between the different documentation organizations, to make it easier to switch between working on different documents;

  3. make it easy to decide where in the tree new documentation should be placed.

In addition, the documentation tree has to accommodate documentation that could be in many different languages and in many different encodings. It is important that the structure of the documentation tree does not enforce any particular defaults or cultural preferences.


6.1 The top level, doc/

There are two types of directory under doc/, each with very specific directory names and meanings.

Directory: share/

Meaning: Contains files that are not specific to the various translations and encodings of the documentation. Contains subdirectories to further categorize the information. For example, the files that comprise the make(1) infrastructure are in share/mk, while the additional SGML support files (such as the FreeBSD extended DocBook DTD) are in share/sgml.

Directory: lang.encoding/

Meaning: One directory exists for each available translation and encoding of the documentation, for example en_US.ISO8859-1/ and zh_TW.Big5/. The names are long, but by fully specifying the language and encoding we prevent any future headaches should a translation team want to provide the documentation in the same language but in more than one encoding. This also completely isolates us from any problems that might be caused by a switch to Unicode.


6.2 The lang.encoding/ directories

These directories contain the documents themselves. The documentation is split into up to three more categories at this level, indicated by the different directory names.

Directory: articles

Contents: Documentation marked up as a DocBook <article> (or equivalent). Reasonably short, and broken up into sections. Normally only available as one HTML file.

Directory: books

Contents: Documentation marked up as a DocBook <book> (or equivalent). Book length, and broken up into chapters. Normally available as both one large HTML file (for people with fast connections, or who want to print it easily from a browser) and as a collection of linked, smaller files.

Directory: man

Contents: For translations of the system manual pages. This directory will contain one or more mann directories, corresponding to the sections that have been translated.

Not every lang.encoding directory will contain all of these directories. It depends on how much translation has been accomplished by that translation team.


6.3 Document specific information

This section contains specific notes about particular documents managed by the FDP.


6.3.1 The Handbook

books/handbook/

The Handbook is written to comply with the FreeBSD DocBook extended DTD.

The Handbook is organized as a DocBook <book>. It is then divided into <part>s, each of which may contain several <chapter>s. <chapter>s are further subdivided into sections (<sect1>) and subsections (<sect2>, <sect3>) and so on.


6.3.1.1 Physical organization

There are a number of files and directories within the handbook directory.

Note: The Handbook's organization may change over time, and this document may lag in detailing the organizational changes. If you have any questions about how the Handbook is organized, please contact the FreeBSD documentation project mailing list.


6.3.1.1.1 Makefile

The Makefile defines some variables that affect how the SGML source is converted to other formats, and lists the various source files that make up the Handbook. It then includes the standard doc.project.mk file, to bring in the rest of the code that handles converting documents from one format to another.


6.3.1.1.2 book.sgml

This is the top level document in the Handbook. It contains the Handbook's DOCTYPE declaration, as well as the elements that describe the Handbook's structure.

book.sgml uses parameter entities to load in the files with the .ent extension. These files (described later) then define general entities that are used throughout the rest of the Handbook.


6.3.1.1.3 directory/chapter.sgml

Each chapter in the Handbook is stored in a file called chapter.sgml in a separate directory from the other chapters. Each directory is named after the value of the id attribute on the <chapter> element.

For example, if one of the chapter files contains:

<chapter id="kernelconfiguration">
...
</chapter>

then it will be called chapter.sgml in the kernelconfiguration directory. In general, the entire contents of the chapter will be held in this file.

When the HTML version of the Handbook is produced, this will yield kernelconfiguration.html. This is because of the id value, and is not related to the name of the directory.

In earlier versions of the Handbook the files were stored in the same directory as book.sgml, and named after the value of the id attribute on the file's <chapter> element. Moving them into separate directories prepares for future plans for the Handbook. Specifically, it will soon be possible to include images in each chapter. It makes more sense for each image to be stored in a directory with the text for the chapter than to try to keep the text for all the chapters, and all the images, in one large directory. Namespace collisions would be inevitable, and it is easier to work with several directories with a few files in them than it is to work with one directory that has many files in it.

A brief look will show that there are many directories with individual chapter.sgml files, including basics/chapter.sgml, introduction/chapter.sgml, and printing/chapter.sgml.

Important: Chapters and/or directories should not be named in a fashion that reflects their ordering within the Handbook. This ordering might change as the content within the Handbook is reorganized; this sort of reorganization should not (generally) include the need to rename files (unless entire chapters are being promoted or demoted within the hierarchy).

Each chapter.sgml file will not be a complete SGML document. In particular, they will not have their own DOCTYPE lines at the start of the files.

This is unfortunate as it makes it impossible to treat these as generic SGML files and simply convert them to HTML, RTF, PS, and other formats in the same way the main Handbook is generated. This would force you to rebuild the Handbook every time you want to see the effect a change has had on just one chapter.


Chapter 7 The Documentation Build Process

This chapter's main purpose is to clearly explain how the documentation build process is organized, and how to affect modifications to this process.

After you have finished reading this chapter you should:


7.1 The FreeBSD Documentation Build Toolset

Here are your tools. Use them every way you can.

  • The primary build tool you will need is make, but specifically Berkeley Make.

  • Package building is handled by FreeBSD's pkg_create. If you are not using FreeBSD, you will either have to live without packages, or compile the source yourself.

  • gzip is needed to create compressed versions of the document. bzip2 compression and zip archives are also supported. tar is supported, but package building demands it.

  • install is the default method to install the documentation. There are alternatives, however.

Note: It is unlikely you will have any trouble finding these last two, they are mentioned for completeness only.


7.2 Understanding Makefiles in the Documentation tree

There are three main types of Makefiles in the FreeBSD Documentation Project tree.


7.2.1 Subdirectory Makefiles

These Makefiles usually take the form of:

SUBDIR =articles
SUBDIR+=books

COMPAT_SYMLINK = en

DOC_PREFIX?= ${.CURDIR}/..
.include "${DOC_PREFIX}/share/mk/doc.project.mk"

In quick summary, the first four non-empty lines define the make variables, SUBDIR, COMPAT_SYMLINK, and DOC_PREFIX.

The first SUBDIR statement, as well as the COMPAT_SYMLINK statement, shows how to assign a value to a variable, overriding any previous value.

The second SUBDIR statement shows how a value is appended to the current value of a variable. The SUBDIR variable is now articles books.

The DOC_PREFIX assignment shows how a value is assigned to the variable, but only if it is not already defined. This is useful if DOC_PREFIX is not where this Makefile thinks it is - the user can override this and provide the correct value.

Now what does it all mean? SUBDIR mentions which subdirectories below this one the build process should pass any work on to.

COMPAT_SYMLINK is specific to compatibility symlinks (amazingly enough) for languages to their official encoding (doc/en would point to en_US.ISO-8859-1).

DOC_PREFIX is the path to the root of the FreeBSD Document Project tree. This is not always that easy to find, and is also easily overridden, to allow for flexibility. .CURDIR is a make builtin variable with the path to the current directory.

The final line includes the FreeBSD Documentation Project's project-wide make system file doc.project.mk which is the glue which converts these variables into build instructions.


7.2.2 Documentation Makefiles

These Makefiles set a bunch of make variables that describe how to build the documentation contained in that directory.

Here is an example:

MAINTAINER=nik@FreeBSD.org

DOC?= book

FORMATS?= html-split html

INSTALL_COMPRESSED?= gz
INSTALL_ONLY_COMPRESSED?=

# SGML content
SRCS=  book.sgml

DOC_PREFIX?= ${.CURDIR}/../../..

.include "$(DOC_PREFIX)/share/mk/docproj.docbook.mk"

The MAINTAINER variable is a very important one. This variable provides the ability to claim ownership over a document in the FreeBSD Documentation Project, whereby you gain the responsibility for maintaining it.

DOC is the name (sans the .sgml extension) of the main document created by this directory. SRCS lists all the individual files that make up the document. This should also include important files in which a change should result in a rebuild.

FORMATS indicates the default formats that should be built for this document. INSTALL_COMPRESSED is the default list of compression techniques that should be used in the document build. INSTALL_ONLY_COMPRESS, empty by default, should be non-empty if only compressed documents are desired in the build.

Note: We covered optional variable assignments in the previous section.

The DOC_PREFIX and include statements should be familiar already.


7.3 FreeBSD Documentation Project make includes

This is best explained by inspection of the code. Here are the system include files:

  • doc.project.mk is the main project include file, which includes all the following include files, as necessary.

  • doc.subdir.mk handles traversing of the document tree during the build and install processes.

  • doc.install.mk provides variables that affect ownership and installation of documents.

  • doc.docbook.mk is included if DOCFORMAT is docbook and DOC is set.


7.3.1 doc.project.mk

By inspection:

DOCFORMAT?=    docbook
MAINTAINER?=    doc@FreeBSD.org

PREFIX?=    /usr/local
PRI_LANG?=  en_US.ISO8859-1

.if defined(DOC)
.if ${DOCFORMAT} == "docbook"
.include "doc.docbook.mk"
.endif
.endif

.include "doc.subdir.mk"
.include "doc.install.mk"

7.3.1.1 Variables

DOCFORMAT and MAINTAINER are assigned default values, if these are not set by the document make file.

PREFIX is the prefix under which the documentation building tools are installed. For normal package and port installation, this is /usr/local.

PRI_LANG should be set to whatever language and encoding is natural amongst users these documents are being built for. US English is the default.

Note: PRI_LANG in no way affects what documents can, or even will, be built. Its main use is creating links to commonly referenced documents into the FreeBSD documentation install root.


7.3.1.2 Conditionals

The .if defined(DOC) line is an example of a make conditional which, like in other programs, defines behavior if some condition is true or if it is false. defined is a function which returns whether the variable given is defined or not.

.if ${DOCFORMAT} == "docbook", next, tests whether the DOCFORMAT variable is "docbook", and in this case, includes doc.docbook.mk.

The two .endifs close the two above conditionals, marking the end of their application.


7.3.2 doc.subdir.mk

This is too long to explain by inspection, you should be able to work it out with the knowledge gained from the previous chapters, and a little help given here.


7.3.2.1 Variables

  • SUBDIR is a list of subdirectories that the build process should go further down into.

  • ROOT_SYMLINKS is the name of directories that should be linked to the document install root from their actual locations, if the current language is the primary language (specified by PRI_LANG).

  • COMPAT_SYMLINK is described in the Subdirectory Makefile section.


7.3.2.2 Targets and macros

Dependencies are described by target: dependency1 dependency2 ... tuples, where to build target, you need to build the given dependencies first.

After that descriptive tuple, instructions on how to build the target may be given, if the conversion process between the target and its dependencies are not previously defined, or if this particular conversion is not the same as the default conversion method.

A special dependency .USE defines the equivalent of a macro.

_SUBDIRUSE: .USE
.for entry in ${SUBDIR}
    @${ECHO} "===> ${DIRPRFX}${entry}"
    @(cd ${.CURDIR}/${entry} && \
    ${MAKE} ${.TARGET:S/realpackage/package/:S/realinstall/install/} DIRPRFX=${DIRPRFX}${entry}/ )
.endfor

In the above, _SUBDIRUSE is now a macro which will execute the given commands when it is listed as a dependency.

What sets this macro apart from other targets? Basically, it is executed after the instructions given in the build procedure it is listed as a dependency to, and it does not adjust .TARGET, which is the variable which contains the name of the target currently being built.

clean: _SUBDIRUSE
    rm -f ${CLEANFILES}

In the above, clean will use the _SUBDIRUSE macro after it has executed the instruction rm -f ${CLEANFILES}. In effect, this causes clean to go further and further down the directory tree, deleting built files as it goes down, not on the way back up.


7.3.2.2.1 Provided targets
  • install and package both go down the directory tree calling the real versions of themselves in the subdirectories (realinstall and realpackage respectively).

  • clean removes files created by the build process (and goes down the directory tree too). cleandir does the same, and also removes the object directory, if any.


7.3.2.3 More on conditionals

  • exists is another condition function which returns true if the given file exists.

  • empty returns true if the given variable is empty.

  • target returns true if the given target does not already exist.


7.3.2.4 Looping constructs in make (.for)

.for provides a way to repeat a set of instructions for each space-separated element in a variable. It does this by assigning a variable to contain the current element in the list being examined.

_SUBDIRUSE: .USE
.for entry in ${SUBDIR}
    @${ECHO} "===> ${DIRPRFX}${entry}"
    @(cd ${.CURDIR}/${entry} && \
    ${MAKE} ${.TARGET:S/realpackage/package/:S/realinstall/install/} DIRPRFX=${DIRPRFX}${entry}/ )
.endfor

In the above, if SUBDIR is empty, no action is taken; if it has one or more elements, the instructions between .for and .endfor would repeat for every element, with entry being replaced with the value of the current element.


Chapter 8 The Website

8.1 Preparation

Get 200MB free disk space. You will need the disk space for the SGML tools, a subset of the CVS tree, temporary build space and the installed web pages. If you already have installed the SGML tools and the CVS tree, you need only ~100MB free disk space.

Note: Make sure your documentation ports are up to date! When in doubt, remove the old ports using pkg_delete(1) command before installing the port. For example, we currently depend on jade-1.2 and if you have installed jade-1.1, please do:

# pkg_delete jade-1.1

Set up a CVS repository. You need the directories www, doc and ports in the CVS tree (plus the CVSROOT of course). Please read the CVSup introduction on how to mirror a CVS tree or parts of a CVS tree.

The essential cvsup collections are: www, doc-all, cvs-base, and ports-base.

These collections require ~105MB free disk space.

A full CVS tree - including src, doc, www, and ports - is currently 940MB.


8.2 Build the web pages from scratch

  1. Create and change directory into a build directory with at least 60MB of free space.

    # mkdir /var/tmp/webbuild
    # cd /var/tmp/webbuild
    
  2. Checkout the SGML files from the CVS tree.

    # cvs -R co www doc
    
  3. Change into the www/en directory, and run the make(1) all target, to create the web pages.

    # cd en
    # make all
    

8.3 Install the web pages into your web server

  1. If you have moved out of the en directory, change back to it.

    # cd path/www/en
    
  2. Run the make(1) install target, setting the DESTDIR variable to the name of the directory you want to install the files to.

    # make DESTDIR=/usr/local/www install
    
  3. If you have previously installed the web pages into the same directory the install process will not have deleted any old or outdated pages. For example, if you build and install a new copy of the site every day, this command will find and delete all files that have not been updated in three days.

    # find /usr/local/www -ctime 3 -print0 | xargs -0 rm
    

8.4 Environment variables

CVSROOT

Location of the CVS tree. Essential.

# CVSROOT=/home/ncvs; export CVSROOT
ENGLISH_ONLY

If set and not empty, the makefiles will build and install only the English documents. All translations will be ignored. E.g.:

# make ENGLISH_ONLY=YES all install

If you want to unset the variable ENGLISH_ONLY and build all pages, including translations, set the variable ENGLISH_ONLY to an empty value:

# make ENGLISH_ONLY="" all install clean
WEB_ONLY

If set and not empty, the makefiles will build and install only the HTML pages from the www directory. All documents from the doc directory (Handbook, FAQ, Tutorials) will be ignored. E.g.:

# make WEB_ONLY=YES all install
NOPORTSCVS

If set, the makefiles will not checkout files from the ports cvs repository. Instead, it will copy the files from /usr/ports (or where the variable PORTSBASE points to).

CVSROOT is an environment variable. You must set it on the command line or in your dot files (e.g., ~/.profile).

WEB_ONLY, ENGLISH_ONLY and NOPORTSCVS are makefile variables. You can set the variables in /etc/make.conf, Makefile.inc, as environment variables on the command line, or in your dot files.


Chapter 9 Translations

This is the FAQ for people translating the FreeBSD documentation (FAQ, Handbook, tutorials, manual pages, and others) to different languages.

It is very heavily based on the translation FAQ from the FreeBSD German Documentation Project, originally written by Frank Gründer and translated back to English by Bernd Warken .

The FAQ is maintained by the Documentation Engineering Team .

9.1. Why a FAQ?
9.2. What do i18n and l10n mean?
9.3. Is there a mailing list for translators?
9.4. Are more translators needed?
9.5. What languages do I need to know?
9.6. What software do I need to know?
9.7. How do I find out who else might be translating to the same language?
9.8. No one else is translating to my language. What do I do?
9.9. I have translated some documentation, where do I send it?
9.10. I am the only person working on translating to this language, how do I submit my translation?
9.11. Can I include language or country specific text in my translation?
9.12. How should language specific characters be included?
9.13. Addressing the reader
9.14. Do I need to include any additional information in my translations?

9.1. Why a FAQ?

More and more people are approaching the freebsd-doc mailing list and volunteering to translate FreeBSD documentation to other languages. This FAQ aims to answer their questions so they can start translating documentation as quickly as possible.

9.2. What do i18n and l10n mean?

i18n means internationalization and l10n means localization. They are just a convenient shorthand.

i18n can be read as “i” followed by 18 letters, followed by “n”. Similarly, l10n is “l” followed by 10 letters, followed by “n”.

9.3. Is there a mailing list for translators?

Yes. Different translation groups have their own mailing lists. The list of translation projects has more information about the mailing lists and web sites run by each translation project.

9.4. Are more translators needed?

Yes. The more people work on translation the faster it gets done, and the faster changes to the English documentation are mirrored in the translated documents.

You do not have to be a professional translator to be able to help.

9.5. What languages do I need to know?

Ideally, you will have a good knowledge of written English, and obviously you will need to be fluent in the language you are translating to.

English is not strictly necessary. For example, you could do a Hungarian translation of the FAQ from the Spanish translation.

9.6. What software do I need to know?

It is strongly recommended that you maintain a local copy of the FreeBSD CVS repository (at least the documentation part) either using CTM or CVSup. The "Staying current with FreeBSD" chapter in the Handbook explains how to use these applications.

You should be comfortable using CVS. This will allow you to see what has changed between different versions of the files that make up the documentation.

[XXX To Do -- write a tutorial that shows how to use CVSup to get just the documentation, check it out, and see what has changed between two arbitrary revisions]

9.7. How do I find out who else might be translating to the same language?

The Documentation Project translations page lists the translation efforts that are currently known about. If others are already working on translating documentation to your language, please do not duplicate their efforts. Instead, contact them to see how you can help.

If no one is listed on that page as translating for your language, then send a message to the FreeBSD documentation project mailing list in case someone else is thinking of doing a translation, but has not announced it yet.

9.8. No one else is translating to my language. What do I do?

Congratulations, you have just started the “FreeBSD your-language-here Documentation Translation Project”. Welcome aboard.

First, decide whether or not you have got the time to spare. Since you are the only person working on your language at the moment it is going to be your responsibility to publicize your work and coordinate any volunteers that might want to help you.

Write an email to the Documentation Project mailing list, announcing that you are going to translate the documentation, so the Documentation Project translations page can be maintained.

If there is already someone in your country providing FreeBSD mirroring services you should contact them and ask if you can have some webspace for your project, and possibly an email address or mailing list services.

Then pick a document and start translating. It is best to start with something fairly small--either the FAQ, or one of the tutorials.

9.9. I have translated some documentation, where do I send it?

That depends. If you are already working with a translation team (such as the Japanese team, or the German team) then they will have their own procedures for handling submitted documentation, and these will be outlined on their web pages.

If you are the only person working on a particular language (or you are responsible for a translation project and want to submit your changes back to the FreeBSD project) then you should send your translation to the FreeBSD project (see the next question).

9.10. I am the only person working on translating to this language, how do I submit my translation?

or

We are a translation team, and want to submit documentation that our members have translated for us?

First, make sure your translation is organized properly. This means that it should drop into the existing documentation tree and build straight away.

Currently, the FreeBSD documentation is stored in a top level directory called doc/. Directories below this are named according to the language code they are written in, as defined in ISO639 (/usr/share/misc/iso639 on a version of FreeBSD newer than 20th January 1999).

If your language can be encoded in different ways (for example, Chinese) then there should be directories below this, one for each encoding format you have provided.

Finally, you should have directories for each document.

For example, a hypothetical Swedish translation might look like:

doc/
    sv_SE.ISO8859-1/
                     Makefile 
                     books/
                           faq/
                               Makefile
                               book.sgml

sv_SE.ISO8859-1 is the name of the translation, in lang.encoding form. Note the two Makefiles, which will be used to build the documentation.

Use tar(1) and gzip(1) to compress up your documentation, and send it to the project.

% cd doc
% tar cf swedish-docs.tar sv_SE.ISO8859-1
% gzip -9 swedish-docs.tar

Put swedish-docs.tar.gz somewhere. If you do not have access to your own webspace (perhaps your ISP does not let you have any) then you can email Documentation Engineering Team , and arrange to email the files when it is convenient.

Either way, you should use send-pr(1) to submit a report indicating that you have submitted the documentation. It would be very helpful if you could get other people to look over your translation and double check it first, since it is unlikely that the person committing it will be fluent in the language.

Someone (probably the Documentation Project Manager, currently Documentation Engineering Team ) will then take your translation and confirm that it builds. In particular, the following things will be looked at:

  1. Do all your files use RCS strings (such as "ID")?

  2. Does make all in the sv_SE.ISO8859-1 directory work correctly?

  3. Does make install work correctly?

If there are any problems then whoever is looking at the submission will get back to you to work them out.

If there are no problems your translation will be committed as soon as possible.

9.11. Can I include language or country specific text in my translation?

We would prefer that you did not.

For example, suppose that you are translating the Handbook to Korean, and want to include a section about retailers in Korea in your Handbook.

There is no real reason why that information should not be in the English (or German, or Spanish, or Japanese, or ...) versions as well. It is feasible that an English speaker in Korea might try to pick up a copy of FreeBSD whilst over there. It also helps increase FreeBSD's perceived presence around the globe, which is not a bad thing.

If you have country specific information, please submit it as a change to the English Handbook (using send-pr(1)) and then translate the change back to your language in the translated Handbook.

Thanks.

9.12. How should language specific characters be included?

Non-ASCII characters in the documentation should be included using SGML entities.

Briefly, these look like an ampersand (&), the name of the entity, and a semi-colon (;).

The entity names are defined in ISO8879, which is in the ports tree as textproc/iso8879.

A few examples include:

Entity: &eacute;

Appearance: é

Description: Small “e” with an acute accent

Entity: &Eacute;

Appearance: É

Description: Large “E” with an acute accent

Entity: &uuml;

Appearance: ü

Description: Small “u” with an umlaut

After you have installed the iso8879 port, the files in /usr/local/share/sgml/iso8879 contain the complete list.

9.13. Addressing the reader

In the English documents, the reader is addressed as “you”, there is no formal/informal distinction as there is in some languages.

If you are translating to a language which does distinguish, use whichever form is typically used in other technical documentation in your language. If in doubt, use a mildly polite form.

9.14. Do I need to include any additional information in my translations?

Yes.

The header of the English version of each document will look something like this:

<!--
     The FreeBSD Documentation Project

     $FreeBSD: doc/en_US.ISO8859-1/books/fdp-primer/translations/chapter.sgml,v 1.5 2000/07/07 18:38:38 dannyboy Exp $
-->

The exact boilerplate may change, but it will always include a $FreeBSD$ line and the phrase The FreeBSD Documentation Project. Note that the $FreeBSD part is expanded automatically by CVS, so it should be empty (just $FreeBSD$) for new files.

Your translated documents should include their own $FreeBSD$ line, and change the FreeBSD Documentation Project line to The FreeBSD language Documentation Project.

In addition, you should add a third line which indicates which revision of the English text this is based on.

So, the Spanish version of this file might start:

<!--
     The FreeBSD Spanish Documentation Project

     $FreeBSD: doc/es_ES.ISO8859-1/books/fdp-primer/translations/chapter.sgml,v 1.3 1999/06/24 19:12:32 jesusr Exp $
     Original revision: 1.11
-->

Chapter 10 Writing style

In order to promote consistency between the myriad authors of the FreeBSD documentation, some guidelines have been drawn up for authors to follow.

Use American English spelling

There are several variants of English, with different spellings for the same word. Where spellings differ, use the American English variant. “color”, not “colour”, “rationalize”, not “rationalise”, and so on.

Note: The use of British English may be accepted in the case of a contributed article, however the spelling must be consistent within the whole document. The other documents such as books, web site, manual pages, etc. will have to use American English.

Do not use contractions

Do not use contractions. Always spell the phrase out in full. “Don't use contractions” would be wrong.

Avoiding contractions makes for a more formal tone, is more precise, and is slightly easier for translators.

Use the serial comma

In a list of items within a paragraph, separate each item from the others with a comma. Separate the last item from the others with a comma and the word “and”.

For example, look at the following:

This is a list of one, two and three items.

Is this a list of three items, “one”, “two”, and “three”, or a list of two items, “one” and “two and three”?

It is better to be explicit and include a serial comma:

This is a list of one, two, and three items.

Avoid redundant phrases

Try not to use redundant phrases. In particular, “the command”, “the file”, and “man command” are probably redundant.

These two examples show this for commands. The second example is preferred.

Use the command cvsup to update your sources.

Use cvsup to update your sources.

These two examples show this for filenames. The second example is preferred.

... in the filename /etc/rc.local...

... in /etc/rc.local...

These two examples show this for manual references. The second example is preferred (the second example uses <citerefentry>).

See man csh for more information.

See csh(1).

Two spaces at the end of sentences

Always use two spaces at the end of sentences, as this improves readability, and eases use of tools such as Emacs.

While it may be argued that a capital letter following a period denotes a new sentence, this is not the case, especially in name usage. “Jordan K. Hubbard” is a good example; it has a capital H following a period and a space, and there certainly is not a new sentence there.

For more information about writing style, see Elements of Style, by William Strunk.


10.1 Style guide

To keep the source for the Handbook consistent when many different people are editing it, please follow these style conventions.


10.1.1 Letter case

Tags are entered in lower case, <para>, not <PARA>.

Text that appears in SGML contexts is generally written in upper case, <!ENTITY...>, and <!DOCTYPE...>, not <!entity...> and <!doctype...>.


10.1.2 Acronyms

Acronyms should generally be spelled out the first time they appear in a book, as in: "Network Time Protocol (NTP)." After the acronym has been defined, you should generally use the acronym only (not the whole term, unless it makes more sense contextually to use the whole term). Usually, acronyms are defined only one per book. But if you prefer, you can also define them the first time they appear in each chapter.

The first three uses of an acronym should be enclosed in <acronym> tags, with a role attribute with the full term defined. This allows a link to the glossary to be created, and for mouseovers to be rendered with the fully expanded term.


10.1.3 Indentation

Each file starts with indentation set at column 0, regardless of the indentation level of the file which might contain this one.

Opening tags increase the indentation level by 2 spaces. Closing tags decrease the indentation level by 2 spaces. Blocks of 8 spaces at the start of a line should be replaced with a tab. Do not use spaces in front of tabs, and do not add extraneous whitespace at the end of a line. Content within elements should be indented by two spaces if the content runs over more than one line.

For example, the source for this section looks something like:

+--- This is column 0
V
<chapter>
  <title>...</title>

  <sect1>
    <title>...</title>

    <sect2>
      <title>Indentation</title>

      <para>Each file starts with indentation set at column 0,
        <emphasis>regardless</emphasis> of the indentation level of the file
        which might contain this one.</para>

      ...   
    </sect2>
  </sect1>
</chapter>

If you use Emacs or XEmacs to edit the files then sgml-mode should be loaded automatically, and the Emacs local variables at the bottom of each file should enforce these styles.

Vim users might want to configure their editor with:

augroup sgmledit
  autocmd FileType sgml set formatoptions=cq2l " Special formatting options
  autocmd FileType sgml set textwidth=70       " Wrap lines at 70 columns
  autocmd FileType sgml set shiftwidth=2       " Automatically indent
  autocmd FileType sgml set softtabstop=2      " Tab key indents 2 spaces
  autocmd FileType sgml set tabstop=8          " Replace 8 spaces with a tab
  autocmd FileType sgml set autoindent         " Automatic indentation
augroup END

10.1.4 Tag style

10.1.4.1 Tag spacing

Tags that start at the same indent as a previous tag should be separated by a blank line, and those that are not at the same indent as a previous tag should not:

<article>
  <articleinfo>
    <title>NIS</title>

    <pubdate>October 1999</pubdate>

    <abstract>
      <para>...
    ...
    ...</para>
    </abstract>
  </articleinfo>

  <sect1>
    <title>...</title>

    <para>...</para>
  </sect1>

  <sect1>
    <title>...</title>

    <para>...</para>
  </sect1>
</article>

10.1.4.2 Separating tags

Tags like <itemizedlist> which will always have further tags inside them, and in fact do not take character data themselves, are always on a line by themselves.

Tags like <para> and <term> do not need other tags to contain normal character data, and their contents begin immediately after the tag, on the same line.

The same applies to when these two types of tags close.

This leads to an obvious problem when mixing these tags.

When a starting tag which cannot contain character data directly follows a tag of the type that requires other tags within it to use character data, they are on separate lines. The second tag should be properly indented.

When a tag which can contain character data closes directly after a tag which cannot contain character data closes, they co-exist on the same line.


10.1.5 White space changes

When committing changes, do not commit changes to the content at the same time as changes to the formatting.

This is so that the teams that convert the Handbook to other languages can quickly see what content has actually changed in your commit, without having to decide whether a line has changed because of the content, or just because it has been refilled.

For example, if you have added two sentences to a paragraph, such that the line lengths on the paragraph now go over 80 columns, first commit your change with the too-long line lengths. Then fix the line wrapping, and commit this second change. In the commit message for the second change, be sure to indicate that this is a whitespace-only change, and that the translation team can ignore it.


10.1.6 Nonbreaking space

Avoid line breaks in places where they look ugly or make it difficult to follow a sentence. Line breaks depend on the width of the chosen output medium. In particular, viewing the HTML documentation with a text browser can lead to badly formatted paragraphs like the next one:

Data capacity ranges from 40 MB to 15
GB.  Hardware compression ...

The general entity &nbsp; prohibits line breaks between parts belonging together. Use nonbreaking spaces in the following places:

  • between numbers and units:

    57600&nbsp;bps
    
  • between program names and version numbers:

    FreeBSD&nbsp;4.7
    
  • between multiword names (use with caution when applying this to more than 3-4 word names like “The FreeBSD Brazilian Portuguese Documentation Project”):

    Sun&nbsp;Microsystems
    

10.2 Word list

The following is a small list of words spelled the way they should be used in the FreeBSD Documentation Project. If the word you are looking for is not in this list, then please consult the O'Reilly word list.

  • 2.2.X

  • 4.X-STABLE

  • CD-ROM

  • DoS (Denial of Service)

  • Ports Collection

  • IPsec

  • Internet

  • MHz

  • Soft Updates

  • Unix

  • disk label

  • email

  • file system

  • manual page

  • mail server

  • name server

  • null-modem

  • web server


Chapter 11 Using sgml-mode with Emacs

Recent versions of Emacs or XEmacs (available from the ports collection) contain a very useful package called PSGML. Automatically invoked when a file with the .sgml extension is loaded, or by typing M-x sgml-mode, it is a major mode for dealing with SGML files, elements and attributes.

An understanding of some of the commands provided by this mode can make working with SGML documents such as the Handbook much easier.

C-c C-e

Runs sgml-insert-element. You will be prompted for the name of the element to insert at the current point. You can use the TAB key to complete the element. Elements that are not valid at the current point will be disallowed.

The start and end tags for the element will be inserted. If the element contains other, mandatory, elements then these will be inserted as well.

C-c =

Runs sgml-change-element-name. Place the point within an element and run this command. You will be prompted for the name of the element to change to. Both the start and end tags of the current element will be changed to the new element.

C-c C-r

Runs sgml-tag-region. Select some text (move to start of text, C-space, move to end of text, C-space) and then run this command. You will be prompted for the element to use. This element will then be inserted immediately before and after your marked region.

C-c -

Runs sgml-untag-element. Place the point within the start or end tag of an element you want to remove, and run this command. The element's start and end tags will be removed.

C-c C-q

Runs sgml-fill-element. Will recursively fill (i.e., reformat) content from the current element in. The filling will affect content in which whitespace is significant, such as within <programlisting> elements, so run this command with care.

C-c C-a

Runs sgml-edit-attributes. Opens a second buffer containing a list of all the attributes for the closest enclosing element, and their current values. Use TAB to navigate between attributes, C-k to remove an existing value and replace it with a new one, C-c C-c to close this buffer and return to the main document.

C-c C-v

Runs sgml-validate. Prompts you to save the current document (if necessary) and then runs an SGML validator. The output from the validator is captured into a new buffer, and you can then navigate from one troublespot to the next, fixing markup errors as you go.

C-c /

Runs sgml-insert-end-tag. Inserts the end tag for the current open element.

Doubtless there are other useful functions of this mode, but those are the ones I use most often.

You can also use the following entries in .emacs to set proper spacing, indentation, and column width for working with the Documentation Project.

    (defun local-sgml-mode-hook
      (setq fill-column 70
            indent-tabs-mode nil
            next-line-add-newlines nil
            standard-indent 4
            sgml-indent-data t)
      (auto-fill-mode t)
      (setq sgml-catalog-files '("/usr/local/share/sgml/catalog")))
    (add-hook 'psgml-mode-hook
      '(lambda () (local-psgml-mode-hook)))
 

Chapter 12 See Also

This document is deliberately not an exhaustive discussion of SGML, the DTDs listed, and the FreeBSD Documentation Project. For more information about these, you are encouraged to see the following web sites.


12.4 DocBook


Appendix A. Examples

This appendix contains example SGML files and command lines you can use to convert them from one output format to another. If you have successfully installed the Documentation Project tools then you should be able to use these examples directly.

These examples are not exhaustive--they do not contain all the elements you might want to use, particularly in your document's front matter. For more examples of DocBook markup you should examine the SGML source for this and other documents, available in the CVSup doc collection, or available online starting at http://www.FreeBSD.org/cgi/cvsweb.cgi/doc/.

To avoid confusion, these examples use the standard DocBook 4.1 DTD rather than the FreeBSD extension. They also use the stock stylesheets distributed by Norm Walsh, rather than any customizations made to those stylesheets by the FreeBSD Documentation Project. This makes them more useful as generic DocBook examples.


A.1 DocBook <book>

Example A-1. DocBook <book>

<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook V4.1//EN">

<book>
  <bookinfo>
    <title>An Example Book</title>
    
    <author>
      <firstname>Your first name</firstname>
      <surname>Your surname</surname>
      <affiliation>
        <address><email>foo@example.com</email></address>
      </affiliation>
    </author>

    <copyright>
      <year>2000</year>
      <holder>Copyright string here</holder>
    </copyright>

    <abstract>
      <para>If your book has an abstract then it should go here.</para>
    </abstract>
  </bookinfo>

  <preface>
    <title>Preface</title>

    <para>Your book may have a preface, in which case it should be placed
      here.</para>
  </preface>
      
  <chapter>
    <title>My first chapter</title>

    <para>This is the first chapter in my book.</para>

    <sect1>
      <title>My first section</title>

      <para>This is the first section in my book.</para>
    </sect1>
  </chapter>
</book>

A.2 DocBook <article>

Example A-2. DocBook <article>

<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook V4.1//EN">

<article>
  <articleinfo>
    <title>An example article</title>

    <author>
      <firstname>Your first name</firstname>
      <surname>Your surname</surname>
      <affiliation>
        <address><email>foo@example.com</email></address>
      </affiliation>
    </author>

    <copyright>
      <year>2000</year>
      <holder>Copyright string here</holder>
    </copyright>

    <abstract>
      <para>If your article has an abstract then it should go here.</para>
    </abstract>
  </articleinfo>

  <sect1>
    <title>My first section</title>

    <para>This is the first section in my article.</para>

    <sect2>
      <title>My first sub-section</title>

      <para>This is the first sub-section in my article.</para>
    </sect2>    
  </sect1>
</article>

A.3 Producing formatted output

This section assumes that you have installed the software listed in the textproc/docproj port, either by hand, or by using the port. Further, it is assumed that your software is installed in subdirectories under /usr/local/, and the directory where binaries have been installed is in your PATH. Adjust the paths as necessary for your system.


A.3.1 Using Jade

Example A-3. Converting DocBook to HTML (one large file)

% jade -V nochunks \  (1)
    -c /usr/local/share/sgml/docbook/dsssl/modular/catalog \ (2)
    -c /usr/local/share/sgml/docbook/catalog \
    -c /usr/local/share/sgml/jade/catalog \
    -d /usr/local/share/sgml/docbook/dsssl/modular/html/docbook.dsl \(3)
    -t sgml (4) file.sgml > file.html (5)
(1)
Specifies the nochunks parameter to the stylesheets, forcing all output to be written to STDOUT (using Norm Walsh's stylesheets).
(2)
Specifies the catalogs that Jade will need to process. Three catalogs are required. The first is a catalog that contains information about the DSSSL stylesheets. The second contains information about the DocBook DTD. The third contains information specific to Jade.
(3)
Specifies the full path to the DSSSL stylesheet that Jade will use when processing the document.
(4)
Instructs Jade to perform a transformation from one DTD to another. In this case, the input is being transformed from the DocBook DTD to the HTML DTD.
(5)
Specifies the file that Jade should process, and redirects output to the specified .html file.

Example A-4. Converting DocBook to HTML (several small files)

% jade \
    -c /usr/local/share/sgml/docbook/dsssl/modular/catalog \ (1)
    -c /usr/local/share/sgml/docbook/catalog \
    -c /usr/local/share/sgml/jade/catalog \
    -d /usr/local/share/sgml/docbook/dsssl/modular/html/docbook.dsl \(2)
    -t sgml (3) file.sgml (4)
(1)
Specifies the catalogs that Jade will need to process. Three catalogs are required. The first is a catalog that contains information about the DSSSL stylesheets. The second contains information about the DocBook DTD. The third contains information specific to Jade.
(2)
Specifies the full path to the DSSSL stylesheet that Jade will use when processing the document.
(3)
Instructs Jade to perform a transformation from one DTD to another. In this case, the input is being transformed from the DocBook DTD to the HTML DTD.
(4)
Specifies the file that Jade should process. The stylesheets determine how the individual HTML files will be named, and the name of the “root” file (i.e., the one that contains the start of the document.

This example may still only generate one HTML file, depending on the structure of the document you are processing, and the stylesheet's rules for splitting output.

Example A-5. Converting DocBook to Postscript

The source SGML file must be converted to a TeX file.

% jade -Vtex-backend \ (1)
    -c /usr/local/share/sgml/docbook/dsssl/modular/catalog \ (2)
    -c /usr/local/share/sgml/docbook/catalog \
    -c /usr/local/share/sgml/jade/catalog \
    -d /usr/local/share/sgml/docbook/dsssl/modular/print/docbook.dsl \(3)
    -t tex (4) file.sgml
(1)
Customizes the stylesheets to use various options specific to producing output for TeX.
(2)
Specifies the catalogs that Jade will need to process. Three catalogs are required. The first is a catalog that contains information about the DSSSL stylesheets. The second contains information about the DocBook DTD. The third contains information specific to Jade.
(3)
Specifies the full path to the DSSSL stylesheet that Jade will use when processing the document.
(4)
Instructs Jade to convert the output to TeX.

The generated .tex file must now be run through tex, specifying the &jadetex macro package.

% tex "&jadetex" file.tex

You have to run tex at least three times. The first run processes the document, and determines areas of the document which are referenced from other parts of the document, for use in indexing, and so on.

Do not be alarmed if you see warning messages such as LaTeX Warning: Reference `136' on page 5 undefined on input line 728. at this point.

The second run reprocesses the document now that certain pieces of information are known (such as the document's page length). This allows index entries and other cross-references to be fixed up.

The third pass performs any final cleanup necessary.

The output from this stage will be file.dvi.

Finally, run dvips to convert the .dvi file to Postscript.

% dvips -o file.ps file.dvi

Example A-6. Converting DocBook to PDF

The first part of this process is identical to that when converting DocBook to Postscript, using the same jade command line (Example A-5).

When the .tex file has been generated you run pdfTeX. However, use the &pdfjadetex macro package instead.

% pdftex "&pdfjadetex" file.tex

Again, run this command three times.

This will generate file.pdf, which does not need to be processed any further.

Notes

[1]

Parameter entities use the Percent symbol.

[2]

This is a shame. Imagine all the problems and hacks (such as Server Side Includes) that could be avoided if they did.

[3]

A short history can be found under http://www.oasis-open.org/committees/docbook/intro.shtml.

[4]

There are other types of list element in DocBook, but we are not concerned with those at the moment.


This, and other documents, can be downloaded from ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/.

For questions about FreeBSD, read the documentation before contacting <questions@FreeBSD.org>.
For questions about this documentation, e-mail <doc@FreeBSD.org>.