For the most part, writing documents using LinuxDoc-Tools is very
simple, and rather like writing HTML. However, there are some caveats to
watch out for. In this section we'll give an introduction on writing
SGML documents. See the file example.sgml for a SGML example
document (and tutorial) which you can use as a model when writing your
own documents. Here we're just going to discuss the various features
of LinuxDoc-Tools, but the source is not very readable as an example. Instead,
print out the source (as well as the formatted output) for
example.sgml so you have a real live case to refer to.
Looking at the source of the example document, you'll notice right off
that there are a number of ``tags'' marked within angle brackets
(< and >). A tag simply specifies the beginning or end
of an element, where an element is something like a section, a paragraph,
a phrase of italicized text, an item in a list, and so on. Using a tag
is like using an HTML tag, or a LaTeX command such as \item or
\section{...}.
As a simple example, to produce this boldfaced text, you would type
As a simple example, to produce <bf>this boldfaced text</bf>, ...
<bf> begins the region of bold text, and
</bf> ends it. Alternately, you can use the abbreviated form
As a simple example, to produce <bf/this boldfaced text/, ...
There are other things to watch out with respect to special characters (that's why you'll notice all of these bizarre-looking ampersand expressions if you look at the source; I'll talk about those shortly).
In some cases, the end-tag for a particular element is optional. For
example, to begin a section, you use the <sect> tag,
however, the end-tag for the section (which could appear at the end of
the section body itself, not just after the name of the section!)
is optional and implied when you start another section of the same depth.
In general you needn't worry about these details; just follow the model
used in the tutorial (example.sgml).
Obviously, the angle brackets are themselves special characters in the
SGML source. There are others to watch out for. For example, let's say
that you wanted to type an expression with angle brackets around it,
as so: <foo>. In order to get the left angle bracket, you
must use the < element, which is a ``macro'' that expands
to the actual left-bracket character. Therefore, in the source, I typed
angle brackets around it, as so: <tt><foo></tt>.
% to produce
%, | to produce |, and so on. For every
special character that might otherwise confuse LinuxDoc-Tools if typed by
itself, there is an ampersand "entity" to represent it. The most
commonly used are:
& for the ampersand (&), < for a left bracket (<),> for a right bracket (>),&etago; for a left bracket with a slash
(</)$ for a dollar sign ($),# for a hash (#),% for a percent (%),˜ for a tilde (~),`` and '' for quotes, or use
&dquot; for ".­ for a soft hyphen (that is, an indication
that this is a good place to break a word for horizontal justification). Here is a complete list of the entities recognized by 0.1. Note that not all back-ends will be able to make anything useful from every entity -- if you see parantheses with nothing between them in the list, it means that the back-end that generated what you're looking at has no replacement for the entity. The ``common'' ones listed above are pretty reliable.
vertical 1/2 fraction
typeset 1/2 fraction
typeset 1/4 fraction
typeset 3/4 fraction
typeset 1/8 fraction
typeset 3/8 fraction
typeset 5/8 fraction
typeset 7/8 fraction
superscript 1
superscript 2
superscript 3
plus sign
plus-or-minus sign
less-than sign
equals sign
greater-than sign
division sign
multiplication sign
currency symbol
symbol for ``pounds''
dollar sign
cent sign
yen sign
number or hash sign
percent sign
ampersand
asterisk
commercial-at sign
left square bracket
backslash
right square bracket
left curly brace
horizontal bar
vertical bar
right curly brace
greek mu (micro prefix)
greek capital omega (Ohm sign)
small superscript circle sign (degree sign)
masculine ordinal
feminine ordinal
section sign
paragraph sign
centered dot
left arrow
right arrow
up arrow
down arrow
copyright
r-in-circle marl
trademark sign
broken vertical bar
logical-negation sign
sung-note sign
exclamation point
inverted exclamation point
double quote
apostrophe (single quote)
left parenthesis
right parenthesis
comma
under-bar
hyphen
period
solidus
colon
semicolon
question mark
interrobang
left guillemot
right guillemot
left single quote
right single quote
left double quote
right double quote
non-breaking space
soft hyphen
While we're on the subject of special characters, we might as well mention
the verbatim ``environment'' used for including literal text in the output
(with spaces and indentation preserved, and so on). The
verb element is used for this; it looks like the following:
<verb>
Some literal text to include as example output.
</verb>
verb environment doesn't allow you to use everything
within it literally. Specifically, you must do the following within
verb environments.
&ero; to get an ampersand, &etago; to get </,\end{verbatim} within a verb
environment, as this is what LaTeX uses to end the verbatim
environment. (In the future, it should be possible to hide the underlying
text formatter entirely, but the parser doesn't support this feature yet.) code environment is much just like the verb environment,
except that horizontal rules are added to the surrounding text, as so:
Here is an example code environment.
You should use the tscreen environment around any verb environments,
as so:
<tscreen><verb>
Here is some example text.
</verb></tscreen>
tscreen is an environment that simply indents the text and sets the
sets the default font to tt. This makes examples look much nicer, both
in the LaTeX and plain text versions. You can use tscreen
without verb, however, if you use any special characters in your
example you'll need to use both of them. tscreen does nothing to
special characters. See example.sgml for examples.
The quote environment is like tscreen, except that it does
not set the default font to tt. So, you can use quote for
non-computer-interaction quotes, as in:
<quote>
Here is some text to be indented, as in a quote.
</quote>
Here is some text to be indented, as in a quote.
Before we get too in-depth with details, we're going to describe the
overall structure of an LinuxDoc-Tools document. Look at
example.sgml for a good example of how a document is set up.
In the document ``preamble'' you set up things such as the title information and document style:
<!doctype linuxdoc system>
<article>
<title>Linux Foo HOWTO
<author>Norbert Ebersol, <tt/norb@baz.com/
<date>v1.0, 9 March 1994
<abstract>
This document describes how to use the <tt/foo/ tools to frobnicate
bar libraries, using the <tt/xyzzy/ relinker.
</abstract>
<toc>
The elements should go more or less in this order. The first line
tells the SGML parser to use the linuxdoc DTD. We'll explain that in
the later section on
How LinuxDoc-Tools Works; for
now just treat it as a bit of necessary magic. The
<article> tag forces the document to use the ``article''
document style.
The title, author, and date tags should be obvious; in the
date tag include the version number and last modification time of
the document.
The abstract tag sets up the text to be printed at the top of the
document, before the table of contents. If you're not going to
include a table of contents (the toc tag), you probably don't
need an abstract.
After the preamble, you're ready to dive into the document. The following sectioning commands are available:
sect: For top-level sections (i.e. 1, 2, and so on.) sect1: For second-level subsections (i.e. 1.1, 1.2, and so on.)sect2: For third-level subsubsections.sect3: For fourth-level subsubsubsections.sect4: For fifth-level subsubsubsubsections.section,
subsection, and so on.
After the sect (or sect1, sect2, etc.) tag comes the
name of the section. For example, at the top of this document, after
the preamble, comes the tag:
<sect>Introduction
<sect2>Sectioning And Paragraphs
<p> tag, as so:
<sect>Introduction
<p>
This is a user's guide to the LinuxDoc-Tools document processing...
Here is the end of the first paragraph.
And we start a new paragraph here.
<p> tags at the beginning of
every paragraph; only at the beginning of the first paragraph after
a sectioning command.
At the end of the document, you must use the tag:
</article>
to tell the parser that you're done with the article element (which
embodies the entire document).
Now we're going to move onto other features of the system. Cross-references are easy. For example, if you want to make a cross-reference to a certain section, you need to label that section as so:
<sect1>Introduction<label id="sec-intro">
See section <ref id="sec-intro" name="Introduction"> for an introduction.
ref tag with the section number labeled
as sec-intro. The name argument to ref is necessary for
groff and HTML translations. The groff macro set used by LinuxDoc-Tools
does not currently support cross-references, and it's often nice to refer
to a section by name instead of number.
For example, this section is Cross-References.
Some back-ends may get upset about special characters in reference labels. In particular, latex2e chokes on underscores (though the latex back end used in older versions of this package didn't). Hyphens are safe.
There is also a url element for Universal Resource Locators, or
URLs, used on the World Wide Web. This element should be used to refer
to other documents, files available for FTP, and so forth. For
example,
You can get the Linux HOWTO documents from
<url url="http://sunsite.unc.edu/mdw/HOWTO/"
name="The Linux HOWTO INDEX">.
url argument specifies the actual URL itself. A link to the
URL in question will be automatically added to the HTML document.
The optional name argument specifies the text that should be anchored to
the URL (for HTML conversion) or named as the description of the
URL (for LaTeX and groff). If no name argument is given, the
URL itself will be used.
A useful variant of this is htmlurl, which suppresses rendering of
the URL part in every context except HTML. What this is useful for
is things like a person's email addresses; you can write
<htmlurl url="mailto:esr@snark.thyrsus.com"
name="esr@snark.thyrsus.com">
Essentially, the same fonts supported by LaTeX are supported
by LinuxDoc-Tools. Note, however, that the conversion to
plain text (through groff) does away with the font
information. So, you should use fonts
as for the benefit of the conversion to LaTeX,
but don't depend on the fonts to get a point across in the plain
text version.
In particular, the tt tag described above can be used to
get constant-width ``typewriter'' font which should be used for
all e-mail addresses, machine names, filenames, and so on.
Example:
Here is some <tt>typewriter text</tt> to be included in the document.
Here is some <tt/typewriter text/ to be included in the document.
Other fonts can be achieved with bf for boldface and em
for italics. Several other fonts are supported as well, but
we don't suggest you use them, because we'll be converting these
documents to other formats such as HTML which may not support them.
Boldface, typewriter, and italics should be all that you need.
There are various kinds of supported lists. They are:
itemize for bulleted lists such as this one.enum for numbered lists.descrip for ``descriptive'' lists. itemize or enum list must be marked
with an item tag. Items in a descrip are marked with tag.
For example,
<itemize>
<item>Here is an item.
<item>Here is a second item.
</itemize>
enum,
<enum>
<item>Here is the first item.
<item>Here is the second item.
</enum>
A descrip list is slightly different, and slightly ugly, but
you might want to use it for some situations:
<descrip>
<tag/Gnats./ Annoying little bugs that fly into your cooling fan.
<tag/Gnus./ Annoying little bugs that run on your CPU.
</descrip>
Annoying little bugs that fly into your cooling fan.
Annoying little bugs that run on your CPU.
The overall goal of LinuxDoc-tools is to be able to produce from one set of masters output that is semantically equivalent on all back ends. Nevertheless, it is sometimes useful to be able to produce a document in slightly different variants depending on back end and version. LinuxDoc-Tools supports this through the <#if> and <#unless> bracketing tags.
These tags allow you to selectively include and uninclude portions of an SGML master in your output, depending on filter options set by your driver. Each tag may include a set of attribute/value pairs. The most common are ``output'' and ``version'' (though you are not restricted to these) so a typical example might look like this:
Some <#if output=latex2e version=drlinux>conditional</#if> text.
Filter options are set in one of two ways. Your format driver sets
the ``output'' option to the name of the back end it uses; thus, in
particular, ``linuxdoc -B latex'' sets
``output=latex2e'', Or you may set an attribute-value pair with
the ``-D'' option of your format driver. Thus, if the above tag were
part of a file a file named ``foo.sgml'', then formatting with either
% linuxdoc -B latex -D version=drlinux foo.sgml
% linuxdoc -B latex foo.sgml
% linuxdoc -B html -D version=drlinux foo.sgml
% linuxdoc -B latex -D private=book foo.sgml
So that you can have conditionals depending on one or more of several values matching, values support a simple alternation syntax using ``|''. Thus you could write:
Some <#if output="latex2e|html" version=drlinux>conditional</#if> text.
The <#unless> tag is the exact inverse of <#if>; it includes when <#if>; would exclude, and vice-versa.
Note that these tags are implemented by a preprocessor which runs before the SGML parser ever sees the document. Thus they are completely independent of the document structure, are not in the DTD, and usage errors won't be caught by the parser. You can seriously confuse yourself by conditionalizing sections that contain unbalanced bracketing tags.
The preprocessor implementation also means that standalone SGML
parsers will choke on LinuxDoc-Tools documents that contain conditionals.
However, you can validity-check them with ``linuxdoc -B check''.
Also note that in order not to mess up the source line numbers in parser error messages, the preprocessor doesn't actually throw away everything when it omits a conditionalized section. It still passes through any newlines. This leads to behavior that may suprise you if you use <if> or <unless> within a <verb> environment, or any other kind of bracket that changes SGML's normal processing of whitespace.
These tags are called ``#if'' and ``#unless'' (rather than ``if'' and ``unless'') to remind you that they are implemented by a preprocessor and you need to be a bit careful about how you use them.
To support automated generation of indexes for book publication of SGML masters, LinuxDoc-Tools supports the <idx> and <cdx> tags. These are bracketing tags which cause the text between them to be saved as an index entry, pointing to the page number on which it occurs in the formatted document. They are ignored by all backends except LaTeX, which uses them to build a .ind file suitable for processing by the TeX utility makeindex.
The two tags behave identically, except that <idx> sets the entry in a normal font and <cdx> in a constant-width one.
If you want to add an index entry that shouldn't appear in the text itself, use the <nidx> and <ncdx> tags.
In order to get proper justification and filling of paragraphs in typeset output, LinuxDoc-Tools includes the ­ entity. This becomes an optional or `soft' hyphen in back ends like latex2e for which this is neaningful.
The bracketing tag <file> can be used to surround filenames in running text. It effectively inserts soft hyphens after each slash in the filename.
One of the advantages of using the <url> and <htmlurl> tags is that they do likewise for long URLs.