HOWTO-HOWTO
Mark Komarinski
List the tools, procedures, and hints to get HOWTO authors up to speed
and writing.
_________________________________________________________________
Table of Contents
[1]Introduction
[2]History
[3]New versions
[4]Comments
[5]Version History
[6]Copyrights and Trademarks
[7]Acknowledgements and Thanks
[8]Background on the LDP and SGML
[9]The LDP
[10]SGML
[11]Why SGML instead of HTML or other formats?
[12]The tools
[13]Getting Started with DocBook
[14]For New Authors
[15]Mailing Lists
[16]Downloading and installing the tools
[17]Writing SGML by hand
[18]Writing SGML using LyX
[19]Writing SGML using PSGML
[20]Getting Started with LinuxDoc
[21]For New Authors
[22]Mailing Lists
[23]Downloading and installing the tools
[24]Writing SGML by hand
[25]CVS
[26]Getting a CVS account
[27]Other CVS repository notes
[28]Updating files and CVS
[29]Distributing your documentation
[30]Before you distribute
[31]Copyright and Licensing issues
[32]Submission to LDP
[33]Style guides
[34]FAQs about the LDP
[35]I want to help the LDP. How can I do this?
[36]I want to publish a collection of LDP documents in a book.
How is the LDP content licensed?
[37]I found an error in an LDP document. Can I fix it?
Introduction
History
This document was started on Aug 26, 1999 by Mark F. Komarinski after
two day's worth of frustration getting tools to work. If even one LDP
author is helped by this, then I did my job.
_________________________________________________________________
New versions
The newest version of this can be found on my homepage
http://www.cgipc.com/~markk/in its SGML source. Other versions may be
found in different formats at the LDP homepage
http://www.linuxdoc.org/.
_________________________________________________________________
Comments
Comments on this HOWTO may be directed to the author
([38]markk@linuxdoc.org).
_________________________________________________________________
Version History
v1.8 (May 17, 2000)
* Corrected errors in LinuxDoc section that didn't render properly.
* Added content about Cygnus tools - thanks to Dan Scott
* Added OpenJade information and link
* More DocBook rendering information - thanks to Greg Ferguson
_________________________________________________________________
Copyrights and Trademarks
(c) 1999-2000 Mark F. Komarinski
This manual may be reproduced in whole or in part, without fee,
subject to the following restrictions:
* The copyright notice above and this permission notice must be
preserved complete on all complete or partial copies
* Any translation or derived work must be approved by the author in
writing before distribution.
* If you distribute this work in part, instructions for obtaining
the complete version of this manual must be included, and a means
for obtaining a complete version provided.
* Small portions may be reproduced as illustrations for reviews or
quotes in other works without this permission notice if proper
citation is given. Exceptions to these rules may be granted for
academic purposes: Write to the author and ask. These restrictions
are here to protect us as authors, not to restrict you as learners
and educators. Any source code (aside from the SGML this document
was written in) in this document is placed under the GNU General
Public License, available via anonymous FTP from the GNU archive.
_________________________________________________________________
Acknowledgements and Thanks
Thanks to everyone that gave comments as I was writing this. This
includes Deb Richardson and Daniel Barlow and other members of the
ldp-discuss list. Some sections I got from the HOWTO Index (available
at many LDP locations) and the sgmltools documentation. There are
pointers to sgmltools and the LDP elsewhere in this document. The
sections on network access to CVS was partially written by Serek
([39]ser@serek.arch.pwr.wroc.pl). Sections on DocBook were written by
Jorge Godoy ([40]godoy@conectiva.com.br). A great deal of thanks to
both of them for their help.
_________________________________________________________________
Background on the LDP and SGML
The LDP
The Linux Documentation Project (LDP) was started to provide new users
a way of getting information quickly about a particular subject. It
not only contains a series of books on administration, networking, and
programming, but has a large number of smaller works on individual
subjects, written by those who have used it. If you want to find out
about printing, you get the Printing HOWTO. If you want to do find out
if your Ethernet card works with Linux, grab the Ethernet HOWTO, and
so on. At first, many of these works were in text or HTML. As time
went on, there had to be a better way of managing these documents. One
that would let you read it from a web page, a text file on a CD-ROM,
or even your hand-held PDA. The answer, as it turns out, is SGML.
_________________________________________________________________
SGML
The Standard Generalized Markup Language (SGML) is a language that is
based on embedding codes within a document. In this way, its similar
to HTML, but there is where any similarities end. The power of SGML is
that unlike WYSIWYG (What You See Is What You Get), you don't define
things like colors, or font sizes, or even some kinds of formatting.
Instead, you define elements (paragraph, section, numbered list) and
let the SGML processor and the end program worry about placement,
colors, fonts, and so on. HTML does the same thing, and is actually a
subset of SGML. SGML has really two parts that make it up. First is
the Structure, which is what is commonly called the DTD, or Document
Type Definition. The DTD defines the relationship between each of the
elements. The DocBook DTD, used to create this document, is an example
of this. The DTD gives a common look and feel to each document that's
created using the DTD. Second is the Content, which is what gets
rendered by the SGML processor and is eventually seen by the user.
This paragraph is content, but so would a graphic image, table,
numbered list, and so on. Content is surrounded by tags to separate
out each element.
_________________________________________________________________
Why SGML instead of HTML or other formats?
SGML provides for more than just formatting. You can automatically
build indexes, table of contents, and links within the document or to
outside. The Jade and OpenJade packages also lets you export (I'll
call it render from here on) SGML to LaTeX, info, text, HTML, and RTF.
From these basic formats, you can then create other formats such as MS
Word, PostScript, PDF and so on. Programs like LyX allow you to write
in TeX format, then export it as SGML and render from SGML to whatever
you chose. In the end, SGML is more concerned about the way elements
work instead of the way they look. A big distinction, and one that
will let you write faster, since you don't have to worry about
placement of paragraphs, font sizes, font types, and so on.
_________________________________________________________________
The tools
In this section, I'll go over some of the tools that you'll need or
want to use to create your own LDP documentation. I'll describe them
here, and better define them later on, along with how to install them.
If you use some other tool to assist in writing LDP, please let me
know and I'll add a blurb here for it.
_________________________________________________________________
Jade
Required - [41]ftp://ftp.jclark.com/pub/jade/jade-1.2.1.tar.gz
Jade is the front-end processor for SGML. It uses the DSSSL and
DocBook DTD to perform the verification and rendering from SGML into
the target format.
_________________________________________________________________
OpenJade
Replacement for Jade - [42]http://openjade.sourceforge.net/
An extension of Jade written by the DSSSL community (see below for
what a DSSSL is). Some applications require jade, but are being
updated to support either software package.
_________________________________________________________________
DSSSL
Required - [43]http://nwalsh.com/docbook/dsssl/db152.zip
The Document Style Semantics and Specification Language tells jade how
to render a SGML document into print or online form. The DSSSL is what
converts a title tag into an
tag in HTML, or bold, 14 point Times
Roman for RTF, for example. Documentation for DSSSL is located at
[44]http://nwalsh.com/docbook/dsssl/db152d.zip. Note that modifying
the DSSSL doesn't modify DocBook itself. It merely changes the way the
rendered text looks. The LDP uses a modified DSSSL that provides for a
table of contents.
_________________________________________________________________
DocBook DTD (version 3.1)
Required - [45]http://www.oasis-open.org/docbook/sgml/3.1/docbk31.zip
The DocBook DTD defines the tags and structure of a DocBook SGML
document. Modifying the DTD, such as adding a new tag, doesn't make it
DocBook anymore.
_________________________________________________________________
sgmltools-lite
Highly Recommended - [46]http://sgmltools-lite.sourceforge.net/
This is the successor to the sgmltools project, which has officially
been disbanded for over a year. Since then, Cees de Groot has created
a slightly different project, which acts as a wrapper to the jade SGML
processor. It hides much of the ugliness of syntax. This author was
able to install the old sgmltools package followed by the
sgmltools-lite and could format this document quite easily. There's
even a man page for sgmltools showing syntax.
_________________________________________________________________
TeX
Optional
TeX (rhymes with blech!) is the markup language of choice for many,
including those in the mathematics world. I still remember many
Calculus exams that were written in TeX. It is also one of the first
markup languages that is still around (the other being the *roff
formats used in man pages). TeX actually follows some of the same
concepts that SGML does. However, TeX renders its files into DVI
(Device Independent) that can then be rendered into another format.
Unfortunately, DVI can't be easily converted into anything other than
printer languages (PostScript, PCL), making it hard to use to generate
HTML. TeX is installed or is available with most Linux distributions.
TeX is available on almost all distributions as LaTeX or TeTeX. Either
should work for you.
_________________________________________________________________
LyX
Optional - [47]http://www.lyx.org/
LyX provides the power of writing SGML with the ease-of-use of a
regular word processor. It's not a WYSIWYG program, but more WYSIWYM
(What You See Is What You Mean) application, since what you see on the
screen isn't necessarily what happens after the SGML processor is done
with it.
_________________________________________________________________
Emacs (PSGML)
Optional - [48]http://www.lysator.liu.se/~lenst/about_psgml/
Emacs has an SGML writing mode called psgml. Anyone with experience
writing in this mode is welcome to e-mail the author of this document.
psgml is a major mode in Emacs designed for editing SGML and XML
documents. It provides "syntax highlighting" or "pretty printing"
features that make SGML tag stand out, a way to insert "tags" other
than typing them by hand, and the ability to validate your document
while writing. For users of Emacs, it's a great way to go, and many
believe it to allow more versatility than any other SGML documentation
tool. It works with DocBook, LinuxDoc and other DTDs equally well.
_________________________________________________________________
WordPerfect 2000
Not recommended - [49]http://www.corel.com/
WordPerfect 2000 for the MS Windows platform has limited support for
SGML and DocBook 3.0. WordPerfect 2000 for Linux has no SGML
capabilities.
_________________________________________________________________
DocBook: The Definitive Guide
Optional (but recommended) - [50]http://www.docbook.org/
This book was released by O'Reilly in October 1999, and is a great
reference to DocBook. I have not found it to be a great practical
book, and much of the emphasis is on XML, but the DocBook tags for
version 3.1 are all listed in a handy format. You can pick it up at
the book vendor of choice. The entire book is also available online at
the above URL.
_________________________________________________________________
Aspell
Optional - [51]http://aspell.sourceforge.net/
This spell checking application can work around SGML tags, and only
spell check the content within the tags. Default spell checkers like
ispell will try to spellcheck the tags, causing errors at every new
tag.
_________________________________________________________________
Cygnus DocBook Tools
Optional (may be Red Hat specific) - [52]http://www.redhat.com/
Red Hat distributes three packages, possibly starting with 6.2, that
include DocBook support and some tools. They provide for only
rendering to HTML and PDF, but they're easily installed if you have
Red Hat, allowing you to focus more on writing than wrestling with the
tools. TeTex 0.9, Jade, and Jadetex must be installed first.
_________________________________________________________________
Getting Started with DocBook
This section covers the new method of writing LDP documentation, using
the DocBook 3.1 DTD. We'll cover getting, installing, and using tools,
along with an introduction to DocBook tags. Since there are over 300
DocBook tags, we won't cover them all here. Really interested readers
can go to http://www.docbook.org for more information.
_________________________________________________________________
For New Authors
If you are a new to the LDP and want to pick up an unmaintained HOWTO
or write a new HOWTO or mini-HOWTO document, contact the HOWTO
coordinator at [53]ldp-discuss@lists.linuxdoc.org. This is to make
sure the HOWTO coordinator can know who is working on what
documentation. Also note that all HOWTO submissions must be in SGML
format using the DocBook 3.1 DTD. The mini-HOWTO submissions may be
made in either SGML or HTML formats, but only SGML-formatted
submissions will be included in printed versions of the HOWTOs.
_________________________________________________________________
Mailing Lists
There are a few mailing lists to subscribe to so you can take part in
how the LDP works. First is ldp-discuss@lists.linuxdoc.org, which is
the main discussion group of the LDP. To subscribe, send a message
with the subject reading "subscribe" to
[54]ldp-discuss-request@lists.linuxdoc.org. To unsubscribe, send an
e-mail with the subject of "unsubscribe" to
ldp-discuss-request@lists.linuxdoc.org.
_________________________________________________________________
Downloading and installing the tools
Manual using jade/openjade
This is the quick and dirty way that should work for all
distributions, no matter what distribution you're using.
1. Create a base directory to store everything such as
/usr/local/sgml. We'll call this $_toolroot form here on.
2. Install Jade, DocBook DTD, and DSSSL such that the base of each is
under $_toolroot (creating $_toolroot/jade-1.2.1, $_toolroot/dtd,
$_toolroot/dssl)
3. You'll need to set the SGML_CATALOG_FILES environment variable to
the catalogs that you have under $_toolroot. You can do this with
the command: $ENV{'SGML_CATALOG_FILES'} =
"$_toolroot/dtd/docbook.cat;$_toolroot/dsssl/docbook/catalog;$_too
lroot/jade-1.2.1/dsssl/catalog"
4. Now you can start using Jade. To create individual HTML files:
$_toolroot/jade-1.2.1/jade/jade -t sgml -i html -d
$_toolroot/dsssl/docbook/html/docbook.dsl howto.sgml
5. To create one large HTML file, add -V nochunks to the jade
command.
_________________________________________________________________
sgmltools
Unlike previous versions of sgmltools, you will require sgmltools
version 2.x for use with DocBook. Since the backend programs have all
changed, you'll also need to forget the sgml2xxx style of programs
(sorry). Since most major distributions ship with sgml 1.x, you'll
need to remove the sgml 1.x package and install either a 2.0 version,
or a CVS version. To get the latest CVS source code version, you can
use the following set of commands:
CVSROOT=:pserver:cvs@cvs.sgmltools.org:/home/cvs
export CVSROOT
cvs login
cvs -z6 get sgmltools
The CVS password is 'cvs'. Once downloaded, You can just use
./compile
make
make install
to install sgmltools. For Red Hat-based systems (using RPM) you can
use the rpmfind command to get the latest sgmltools. The rpmfind
program is available at http://www.rpmfind.net/. Make sure you get
sgmltools and not sgml-tools, as the latter is sgml-tools 1.0.9. For
Debian-based systems, apt-get will retrieve the right package for you:
# apt-get install sgmltools
As with the RedHat, be sure to get sgmltools and not sgml-tools.
_________________________________________________________________
Cygnus DocBook Tools
These tools are provided with Red Hat 6.2. Make sure the following
packages are installed:
* sgml-common
* docbook
* stylesheets
Red Hat has the latest version on their web site:
[55]http://www.redhat.com/support/errata/RHBA-2000022-01.html.
Download/get/sneakernet the RPMs to your machine and install in the
usual manner (become root, then rpm -Uvh filename). Once the RPMs are
installed, you can use the following commands to render DocBook:
db2html filename
Renders DocBook into HTML. A subdirectory with the filename (minus the
.sgml extension) is created and the HTML files are placed there.
db2pdf filename
Renders DocBook into a PDF file.
_________________________________________________________________
Writing SGML by hand
Must of this is covered by Jorge Godoy's Using DocBook document. Those
interested can read it at
[56]http://metalab.unc.edu/godoy/using-docbook/using-docbook.html for
writing DocBook using your favorite text editor.
_________________________________________________________________
Writing SGML using LyX
New documents
You can easily start a new HOWTO using LyX. Use the File->New from
template... menu command to bring up the template listings. Select
Templates on the right side of the screen, then select
docbook_template.lyx in the file listing. Select OK, and you'll have a
new document. Fill in the items, such as title, abstract, and author
name, then start writing.
_________________________________________________________________
Existing documents
If you have an already-existing LyX, TeX, or text document, you can
import it into LyX with the File->import command. Once the file is
imported, go to Layout->Document... In the popup window, under Style,
select SGML (DocBook Article). You'll be asked if you want to convert
all text over, and say Yes. You will need to reapply most tags, but
it's a fairly simple matter of selecting text and changing the style.
Many LyX functions have a keyboard shortcut to assist you.
_________________________________________________________________
Exporting documents to SGML
Once your document is written or converted, save it in LyX format.
This will allow you to edit future versions easily. Then, go to
File->Export->as DocBook... and the file will be exported in DocBook.
_________________________________________________________________
Writing SGML using PSGML
Not written
Unfortunately, I don't use Emacs. If you use PSGML for
writing/validating SGML, please e-mail the author your directions and
I'll be happy to add them here as a service for other users.
_________________________________________________________________
Getting Started with LinuxDoc
This section shows how to get involved in writing your own LDP
documentation. Getting and setting up the tools, making contact with
the LDP in general, and distributing what you know to all the Linux
users out there.
_________________________________________________________________
For New Authors
If you are a new to the LDP and want to pick up an unmaintained HOWTO
or write a new HOWTO or mini-HOWTO document, contact the HOWTO
coordinator at ldp-discuss@lists.linuxdoc.org. This is to make sure
the HOWTO coordinator can know who is working on what documentation.
Also note that all HOWTO submissions must be in SGML format (using
DocBook or LinuxDoc DTD). The mini-HOWTO submissions may be made in
either SGML or HTML formats, but only SGML-formatted submissions will
be included in printed versions of the HOWTOs.
_________________________________________________________________
Mailing Lists
There are a few mailing lists to subscribe to so you can take part in
how the LDP works. First is ldp-discuss@lists.linuxdoc.org, which is
the main discussion group of the LDP. To subscribe, send a message
with the subject reading "subscribe" to
ldp-discuss-request@lists.linuxdoc.org. To unsubscribe, send an e-mail
with the subject of "unsubscribe" to
ldp-discuss-request@lists.linuxdoc.org.
_________________________________________________________________
Downloading and installing the tools
sgmltools
Download the sgmltools package from http://www.sgmltools.org/, or
directly from your distribution. The source files from sgmltools.org
is in source code format, so you will have to compile the source code
for your machine. Using a pre-built package for your distribution is
easier, as you don't have to compile it and potentially run into
compilation issues (that is, if you're not a coder). With RedHat, the
sgmltools is included with the distribution. If not, you can download
it from ftp.redhat.com or any of its mirrors as part of the main
distribution. If you're using Debian, it too has sgmltools in the
standard distribution. If you don't have the package installed, you
can use the apt-get command to download and install the package for
you:
# apt-get install sgml-tools
For more information on the Debian package, you can look at
http://www.debian.org/Packages/stable/text/sgml-tools.html If
compiling from source, all you need to do is:
# tar -zxvf sgmltools-x.x.x.tar.gz
# cd sgmltools-x.x.x
# ./configure
# make
# make install
Replace sgmltools-x.x.x with the actual version of the sgmltools
package you're using. The current version as of this writing that
supports LinuxDoc is 1.0.9. The version that supports DocBook is
2.0.2. Both are available at the above web site. Once the tools are
installed, you have a number of commands available to you.
* sgmlcheck file.sgml- Checks the syntax of a given document.
* sgml2html file.sgml- Converts an SGML file into HTML. Creates a
file.html file that contains the Table Of Contents, then creates
file-x.html files where x is the section number.
* sgml2rtf file.sgml- Converts an SGML file into Rich Text Format
(RTF). Creates two files, the first being file.rtf that contains
the TOC, and a file-0.rtf that contains all the sections.
* sgml2txt file.sgml- Converts an SGML file into ASCII text. The TOC
and all sections are all put into file.txt.
* sgml2info file.sgml- Blah SGML blah INFO, used by the info
command. All output is sent to file.info.
* sgml2latex file.sgml- Blah SGML blah TeX.
* sgml2lyx file.sgml- SGML yadda LyX graphical editor. This is great
if you have pre-generated SGML files and want to convert them for
use in LyX.
_________________________________________________________________
Writing SGML by hand
Much like HTML, you can write SGML by hand, once you know all the
markup codes you want to use. This section will go over as many of
these codes as possible, along with practical examples of each. A nice
place to start would be the SGML source for this document, which is
available at the web site in the Introduction. As the SGML may be
processed differently depending on the file format you go to, I'll try
to list some things to know about as you're writing.
_________________________________________________________________
Starting out
To start a new document, create a new file in your favorite ASCII
editor and start with this: This defines
the document type (LinuxDoc in our case) that the SGML processor will
use when it renders the file in an output format. Nothing is rendered
from this tag. Next you need to enclose the rest of your work in
and tags. This signifies the start of the content
(or article, eh?). If you're familiar with HTML, this is similar to
enclosing all your content with and .
_________________________________________________________________
Header information
The first part of the content should contain general information about
the rest of the content. This would be similar to the first few pages
of a book, where you have a title page (title of the work, author,
date of publication, table of contents, and so on). The title of the
content is enclosed in and tags. The author is
specified in and tags. The date uses and
. The two remaining sections are the and
tags, which provide an executive summary of what the content is about,
and the tag, which specifies the location of the table of
contents. The TOC is automatically generated by the SGML processor.
We'll get into sections later on. Now, how does it all look together?
Taking a nice bit of SGML code (that is, what was used to create this
document) you'll see:
HOWTO HOWTO Mark F. Komarinski v1.1, 14 December 1999 List the tools, procedures, and hints to get HOWTO authors up to spee
d writing.
This bit of content created the main page you see when you look at
this document in RTF or HTML format, listing all the information on
one page.
_________________________________________________________________
Sections
In order to build the Table of Contents, you need to have something to
build with. Sections in the case of SGML is the same as chapters in
traditional publishing. You have multiple sections, and each section
can have a subsection, and each of those can have a subsection and so
on. Starting your document with sections is great as it lets you
create an outline of the major topics you want to cover. You can then
break down these major sections into gradually smaller sections, until
you have a nugget of information you can write about in a few short
paragraphs. In writing this document, I actually started this way.
Sections are one of the few sets of SGML tags that don't require to be
closed. That is, there is no tag. Nor do you have to worry
about numbering. The SGML processor will handle it all when you render
the SGML into something else. Sections are started with tags. A
new section is started with each tag. The first section is
numbered 1. Creating subsections (like 1.1) is done with the
tag. It also starts with 1. Sub subsections (1.1.1) is done with the
tag, and also starts with 1. When the SGML processor comes
across the tag, it runs through the rest of the document and
builds the Table Of Contents based on the number of section tags
within it. Sections are numbered and listed in the TOC and then used
in the rest of the document. Sub subsections (1.1.1) do not show up in
the TOC, but are put in emphasized text if possible.
_________________________________________________________________
Normal paragraphs
Writing paragraphs of content is just like in HTML. Use a
tag to
specify a new line, and start writing. SGML will ignore whitespace
such as tabs, multiple spaces, and newlines. When SGML comes across a
tag, it starts a new paragraph. Proper SGML has you put in a
to end the paragraph.
_________________________________________________________________
Enhanced Text
Every now and then you need a touch of text to stand out from the
others. Either to highlight code or to list a command name. The first
(emphasizing text) is done with and tags. Typewriter text
(the second example) is done with and tags.
_________________________________________________________________
Lists
There are two forms of doing lists under SGML. First is an enumerated
list, where each item in the list is numbered (like sections) starting
with 1. 1. This is the first entry in the enumerated list. 2. This is
the second. 3. Third. The code for the above list looks like this:
This is the first entry in the enumerated list.
This is the second. Third. The tag
specifies that the following items are going to be enumerated. The
other method of writing lists is itemized, where each item merely has
a star, or circle, or dot, or some other method of itemizing each
item.
* This is the first entry in the itemized list
* This is the second
* Third
The above code looks like this in raw SGML:
This is the first entry in the itemized list
This is the second
Third
As you can see, the tag is the same for enumerated and itemized
lists. A third form of lists is the description lists. This has a term
being described, and the phrase that describes it. LDP The Linux
Documentation Project SGML Standard Generalized Markup Language The
code to create the above descriptions is: LDPThe
Linux Documentation Project SGMLStandard Generalized Markup
Language This isn't quite the same as itemized or
enumerated lists, but you have the entire list surrounded by a tag
( and ) and each item in the line that is a word
being defined is enclosed in and . The remainder of the
line is taken to be the definition of the word.
_________________________________________________________________
Verbatim text
Sometimes you just need to print some text the way you write it. For
this, you can use the and tags to enclose a paragraph
in verbatim mode. Spaces, carriage returns, and other literal text
(including special characters) are preserved until the . This
is verbatim text.
_________________________________________________________________
URLs
Also in SGML is the ability to handle Universal Resource Locators
(URL) of any kind. Note that this would only work when exported to
HTML mode, but other formats may use them as well. A URL doesn't have
an end tag, but puts its information within the tag itself. Here
is a URL that points to the LDP homepage: http://www.linuxdoc.org/.
And here's the code to create it: The
url=\"{}http://www.linuxdoc.org/\"{} tells the browser where to go,
while the contents of the name=\"{}http://www.linuxdoc.org/\"{} tells
the browser what to print out to the screen. In this case, the two are
similar, but I could create a URL tag that looks like this: And then looks on the page
like this: LDP. However, good form suggests that you duplicate the URL
in the name portion. The reason for this is if you're using something
like Text or RTF output, the above tag would have no meaning. you
wouldn't know what URL to use.
_________________________________________________________________
References
While URLs are great for linking to content outside the LDP document
you're working on, it's not that great for linking within the content
itself. For this, you use the