SGML Markup

SGML Markup This chapter describes the three 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 freebsd-doc@freebsd.org. 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. 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 documention, 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. 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" Sectional elements An HTML document is normally split in to 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. Normal HTML document structure <html> <head> <title>The document's title</title> </head> <body> … </body> </html> Block elements 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. <sgmltag>h1</sgmltag>, <sgmltag>h2</sgmltag>, etc. Use: First section

This is the heading for the first section

This is the heading for the first sub-section

This is the heading for the second section

]]> 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, preceeding it. Leaving gaps in the numbering is to be avoided. Bad ordering of <sgmltag>h<replaceable>n</replaceable></sgmltag> elements Use: First section

Sub-section

]]> Paragraphs HTML supports a single paragraph element, p. <sgmltag>p</sgmltag> Use: This is a paragraph. It can contain just about any other element.

]]> Block quotations A block quotation is an extended quotation from another document that should not appear within the current paragraph. <sgmltag>blockquote</sgmltag> Use: A small excerpt from the US Constitution;

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.

]]> 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 proceeded 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. <sgmltag>ul</sgmltag> and <sgmltag>ol</sgmltag> Use: An unordered list. Listitems will probably be preceeded by bullets.

First item
Second item
Third item

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

This is the first item. It only has one paragraph.
This is the first paragraph of the second item.

This is the second paragraph of the second item.
This is the first and only paragraph of the third item.

]]> Definition lists with <sgmltag>dl</sgmltag> Use:

Term 1

Paragraph 1 of definition 1.

Paragraph 2 of definition 1.

Term 2

Paragraph 1 of definition 2.

Term 3

Paragraph 1 of definition 3. Note that the <p> element is not required in the single paragraph case.

]]> 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 in to one, and line breaks in the text are significant. In order to do this, wrap the content in the pre element. <sgmltag>pre</sgmltag> You could use pre to mark up an e-mail message; From: nik@freebsd.org To: freebsd-doc@freebsd.org Subject: New documentation available There's a new copy of my primer for contributers to the FreeBSD Documentation Project available at Comments appreciated. N ]]> Tables 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. Simple use of <sgmltag>table</sgmltag> Use: This is a simple 2x2 table.

Top left cell	Top right cell
Bottom left cell	Bottom right cell

]]> 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. Using <literal>rowspan</literal> Use: One tall thin cell on the left, two short cells next to it on the right.

Long and thin
	Top cell	Bottom cell

]]> Using <literal>colspan</literal> Use: One long cell on top, two short cells below it.

Top cell
Bottom left cell	Bottom right cell

]]> Using <literal>rowspan</literal> and <literal>colspan</literal> together Use: On a 3x3 grid, the top left block is a 2x2 set of cells merged in to one. The other cells are normal.

Top left large cell		Top right cell
Top left large cell		Middle right cell
Bottom left cell	Bottom middle cell	Bottom right cell

]]> In-line elements Emphasising 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. <sgmltag>em</sgmltag> and <sgmltag>strong</sgmltag> Use: This has been emphasised, while this has been strongly emphasised.

]]> 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. <sgmltag>b</sgmltag> and <sgmltag>i</sgmltag> This is in bold, while this is in italics.

]]> Indicating fixed pitch text If you have content that should be rendered in a fixed pitch (typewriter) typeface, use tt (for “teletype”). <sgmltag>tt</sgmltag> Use: This document was originally written by Nik Clayton, who can be reached by e-mail as nik@freebsd.org.

]]> Content size You can indicate that content should be shown in a larger or smaller font. There are three ways of doing this. 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. 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. Use font with the size attribute set to a number between 1 and 7. The default font size is 3. This approach is deprecated. <sgmltag>big</sgmltag>, <sgmltag>small</sgmltag>, and <sgmltag>font</sgmltag> The following fragments all do the same thing. This text is slightly smaller. But this text is slightly bigger.

This text is slightly smaller. But this text is slightly bigger

This text is slightly smaller. But this text is slightly bigger.

]]> Links Links are also in-line elements. 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 colour, different mouse cursor when over the link, and so on). Using <literal><a href="..."></literal> Use: More information is available at the FreeBSD web site.

]]> These links will take the user to the top of the chosen document. 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. Using <literal><a name="..."></literal> Use: This paragraph can be referenced in other links with the name para1.

]]> 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. Linking to a named part of another document Assume that the para1 example resides in a document called foo.html. More information can be found in the first paragraph of foo.html.

]]> 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 preceeding #). Linking to a named part of another document Assume that the para1 example resides in this document More information can be found in the first paragraph of this document.

]]> DocBook DocBook was designed by the Davenport Group to be a DTD for writing technical documentation. As such, and unlike LinuxDoc and HTML, DocBook is very heavily orientated towards markup that describes what something is, rather than describing how it should be presented. <literal>formal</literal> vs. <literal>informal</literal> 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 information 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. 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. 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 Nik Clayton nik@freebsd.org. Formal Public Identifier (FPI) In compliance with the DocBook guidelines for writing FPIs for DocBook customisations, the FPI for the FreeBSD extended DocBook DTD is; PUBLIC "-//FreeBSD//DTD DocBook V3.1-Based Extension//EN" Sectional elements DocBook contains a number of elements for marking up the structure of a book. Generally, the top level (first) element will be book. A book is organised into chapters. This is a mandatory requirement. There may be parts between the book and the chapter to provide another layer of organisation. 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. 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. Boilerplate <sgmltag>book</sgmltag> with <sgmltag>bookinfo</sgmltag> <book> <bookinfo> <title>Your title here</title> <author> <firstname>Your first name</firstname> <surname>Your surname</surname> <affiliation> <address><email>Your e-mail address</email></address> </affiliation> </author> <copyright> <year>1998</year> <holder role="mailto:your e-mail address">Your name</holder> </copyright> <pubdate role="rcs">$Date$</pubdate> <releaseinfo>$Id$</releaseinfo> <abstract> <para>Include an abstract of the book's contents here.</para> </abstract> </bookinfo> … </book> Indicating chapters Use chapter to mark up your chapters. Each chapter has a mandatory title. A simple chapter The chapter's title ... ]]> A chapter can not be empty, it must contain elements in addition to title. If you need to include an empty chapter then just use an empty paragraph. Empty chapters This is an empty chapter ]]> Sections below chapters Chapters can be broken up into sections, subsections, and so on. 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. Sections in chapters A sample chapter Some text in the chapter. First section (1.1) ... Second section (1.2) First sub-section (1.2.1) First sub-sub-section (1.2.1.1) ... Second sub-section (1.2.2) ... ]]> Subdividing using <sgmltag>part</sgmltag>s You can introduce another layer of organisation between book and chapter with one or more parts. Introduction Overview ... What is FreeBSD? ... History ... ]]> Block elements 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. <sgmltag>para</sgmltag> Use: This is a paragraph. It can contain just about any other element. ]]> Appearance: This is a paragraph. It can contain just about any other element. 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). <sgmltag>blockquote</sgmltag> Use: A small excerpt from the US Constitution;

Preamble to the Constitution of the United States</para> <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>]]></programlisting> <para>Appearance:</para> <blockquote> <title>Preamble to the Constitution of the United States Copied from a web site somewhere 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.

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. <sgmltag>warning</sgmltag> Use: Installing FreeBSD may make you want to delete Windows from your harddisk. ]]> Installing FreeBSD may make you want to delete Windows from your harddisk. 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 procedureThere are other types of list element in DocBook, but we're not concerned with those at the moment. itemizedlist and orderedlist are similar to the 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 analagous to HTMLs li tags. However, unlike HTML they are required. procedure is slightly different. It consists of steps, which may in turn consists of more steps or substeps. Each step contains block elements. <sgmltag>itemizedlist</sgmltag>, <sgmltag>orderedlist</sgmltag>, and <sgmltag>procedure</sgmltag> Use: This is the first itemized item. This is the second itemized item. This is the first ordered item. This is the second ordered item. ]]> Appearance: This is the first itemized item. This is the second itemized item. This is the first ordered item. This is the second ordered item. 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 closing tag should appear on the same line as the last line of the output, otherwise a spurious blank line will be included. <sgmltag>programlisting</sgmltag> Use: When you have finished, your program should look like this; #include <stdio.h> int main(void) { printf("hello, world\n"); }]]> 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"); } There is a mechanism within DocBook for referring to sections of a previously occuring programlisting, called callouts (see programlistingco for more information). I don't fully understand (i.e., have never used) this feature, so can't document it here. For the mean time, you can include line numbers within the content, and then refer to them later on in your description. That will change, as soon as I find the time to understand and document callouts. 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. <sgmltag>informaltable</sgmltag> Use: 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 ]]> 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 If you don't 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">). Tables where <literal>frame="none"</literal> 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 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 in to play here. informalexample Most of the time these examples will occur “mid-flow” as it were, and you won't need to put a title on them. So, most of the time, the outermost element will be informalexample. For those times when you do need to include a title on the example, use example. 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 OS, 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. &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. <sgmltag>informalexample</sgmltag>, <sgmltag>screen</sgmltag>, <sgmltag>prompt</sgmltag>, and <sgmltag>userinput</sgmltag> Use: &prompt.user; ls -1 foo1 foo2 foo3 &prompt.user; ls -1 | grep foo2 foo2 &prompt.user; su Password: &prompt.root; cat foo2 This is the file called 'foo2' ]]> Appearance: &prompt.user; ls -1 foo1 foo2 foo3 &prompt.user; ls -1 | grep foo2 foo2 &prompt.user; su Password: &prompt.root; cat foo2 This is the file called 'foo2' 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. In-line elements Emphasising information When you want to emphasise 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. <sgmltag>emphasis</sgmltag> Use: FreeBSD is without doubt the premiere Unix like operating system for the Intel architecture.]]> Appearance: FreeBSD is without doubt the premiere Unix like operating system for the Intel architecture. 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 it's 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 it's 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 V3.1-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 a command's options. This can be confusing, and sometimes the choice is not always clear. Hopefully this example makes it clearer. Applications, commands, and options. Use: Sendmail is the most widely used Unix mail application. Sendmail includes the sendmail 8 , &man.sendmail.8;, and &man.newaliases.8; programs. One of the command line parameters to sendmail 8 , , will display the current status of messages in the mail queue. Check this on the command line by running sendmail -bp.]]> 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 , , will display the current status of messages in the mail queue. Check this on the command line by running sendmail -bp. Notice how the &man.command.section; notation is easier to follow. Files, directories, extensions Whenever you wish to refer to the name of a file, a directory, or a file extension, use filename. <sgmltag>filename</sgmltag> Use: 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.]]> 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. 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. <sgmltag>devicename</sgmltag> Use: 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.]]> 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. 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="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 seperated by colons. <sgmltag>hostid</sgmltag> and roles Use: 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 in existence. A typical MAC address looks like 08:00:20:87:ef:d0.]]> 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. 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. <sgmltag>username</sgmltag> Use: To carry out most system administration functions you will need to be root.]]> Appearance: To carry out most system administration functions you will need to be root. Describing <filename>Makefile</filename>s 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. <sgmltag>maketarget</sgmltag> and <sgmltag>makevar</sgmltag> Use: 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.]]> 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. 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. <sgmltag>literal</sgmltag> Use: 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.]]> 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. Showing items that the user <emphasis>must</emphasis> 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 can not 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. <sgmltag>replaceable</sgmltag> Use: &prompt.user; man command ]]> Appearance: &prompt.user; 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: 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.]]> 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. Links Links are also in-line elements. Linking to other parts of the same document Linking within the same document requires you to 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. <literal>id on chapters and sections</literal> Introduction This is the introduction. It contains a subsection, which is identified as well. Sub-sect 1 This is the subsection. ]]> 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. <sgmltag>anchor</sgmltag> This paragraph has an embedded link target in it. It won't show up in the document.]]> 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 occured 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. Using <sgmltag>xref</sgmltag> Assume that this fragment appears somewhere in a document that includes the id example; More information can be found in . More specific information can be found in .]]> The text of the link will be generated automatically, and will look like (emphasised 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. This means that you can not use xref to link to an id attribute on an anchor element. The anchor has no content, so the xref can not 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. Using <sgmltag>link</sgmltag> Assume that this fragment appears somewhere in a document that includes the id example. More information can be found in the first chapter. More specific information can be found in FreeBSD home page instead.]]> Appearance: Of course, you could stop reading this document and go to the FreeBSD home page instead. * LinuxDoc LinuxDoc is an adaptation of the QWERTZ DTD, first adopted by the Linux Documentation Project, and subsequently adopted by the FreeBSD Documentation Project. The LinuxDoc DTD contains primarily appearance related markup rather than content related markup (i.e., it describes what something looks like rather than what it is). Both the FreeBSD Documentation Project and the Linux Documentation Project are migrating from the LinuxDoc DTD to the DocBook DTD. The LinuxDoc DTD is available from the ports collection in the textproc/linuxdoc category.