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<chapter id="xhtml-markup">
  <title><acronym>XHTML</acronym> Markup</title>

  <sect1 id="xhtml-markup-introduction">
    <title>Introduction</title>

    <para>This chapter describes usage of the <acronym>XHTML</acronym>
      markup language used for the &os; web site.</para>

    <para><acronym>XHTML</acronym> is the <acronym>XML</acronym>
      version of the HyperText Markup Language, the markup language of
      choice on the World Wide Web.  More information can be found at
      <ulink url="http://www.w3.org/"></ulink>.</para>

    <para><acronym>XHTML</acronym> is used to mark up pages on the
      &os; web site.  It is usually not used to mark up other
      documentation, since DocBook offers a far richer set of elements
      from which to choose.  Consequently, <acronym>XHTML</acronym>
      pages will normally only be encountered when writing for the web
      site.</para>

    <para><acronym>HTML</acronym> has gone through a number of
      versions.  The <acronym>XML</acronym>-compliant version
      described here is called <acronym>XHTML</acronym>.  The latest
      widespread version is <acronym>XHTML</acronym> 1.0, available in
      both <emphasis>strict</emphasis> and
      <emphasis>transitional</emphasis> variants.</para>

    <para>The <acronym>XHTML</acronym> <acronym>DTDs</acronym> are
      available from the Ports&nbsp;Collection in
      <filename role="package">textproc/xhtml</filename>.  They are
      automatically installed as part of the <filename
	role="package">textproc/docproj</filename> port.</para>

    <note>
      <para>This is <emphasis>not</emphasis> an exhaustive list of
	elements, since that would just repeat the documentation for
	<acronym>XHTML</acronym>.  The aim is to list those elements
	most commonly used.  Please post questions about elements or
	uses not covered here to the &a.doc;.</para>
    </note>

    <note>
      <title>Inline Versus Block</title>

      <para>In the remainder of this document, when describing
	elements, <emphasis>inline</emphasis> means that the element
	can occur within a block element, and does not cause a line
	break.  A <emphasis>block</emphasis> element, by comparison,
	will cause a line break (and other processing) when it is
	encountered.</para>
    </note>
  </sect1>

  <sect1 id="xhtml-markup-fpi">
    <title>Formal Public Identifier (<acronym>FPI</acronym>)</title>

    <para>There are a number of <acronym>XHTML</acronym>
      <acronym>FPI</acronym>s, depending upon the version, or
      <emphasis>level</emphasis> of <acronym>XHTML</acronym> to which
      a document conforms.  Most XHTML documents on the FreeBSD web
      site comply with the transitional version of
      <acronym>XHTML</acronym> 1.0.</para>

    <programlisting>PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"</programlisting>
  </sect1>

  <sect1 id="xhtml-markup-sectional-elements">
    <title>Sectional Elements</title>

    <para>An <acronym>XHTML</acronym> document is normally split into
      two sections.  The first section, called the
      <emphasis>head</emphasis>, 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
      <emphasis>body</emphasis>, contains the content that will be
      displayed to the user.</para>

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

    <example>
      <title>Normal <acronym>XHTML</acronym> Document
	Structure</title>

      <programlisting>&lt;html xmlns="http://www.w3.org/1999/xhtml">
  &lt;head>
	  &lt;title><replaceable>The Document's Title</replaceable>&lt;/title>
  &lt;/head>

  &lt;body>

    &hellip;

  &lt;/body>
&lt;/html></programlisting>
    </example>
  </sect1>

  <sect1 id="xhtml-markup-block-elements">
    <title>Block Elements</title>

    <sect2 id="xhtml-markup-block-elements-headings">
      <title>Headings</title>

      <para><acronym>XHTML</acronym> has tags to denote headings in
	the document at up to six different levels.</para>

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

      <para>The element's content is the text of the heading.</para>

      <example>
	<title><sgmltag>h1</sgmltag>, <sgmltag>h2</sgmltag>,
	  and Other Header Tags</title>

	<para>Usage:</para>

	<programlisting><![CDATA[<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 -->]]></programlisting>
      </example>

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

      <example>
	<title>Bad Ordering of
	  <sgmltag>h<replaceable>n</replaceable></sgmltag>
	  Elements</title>

	<para>Usage:</para>

	<programlisting><![CDATA[<h1>First section</h1>

<!-- Document introduction -->

<h3>Sub-section</h3>

<!-- This is bad, <h2> has been left out -->]]></programlisting>
      </example>
    </sect2>

    <sect2 id="xhtml-markup-block-elements-paragraphs">
      <title>Paragraphs</title>

      <para><acronym>XHTML</acronym> supports a single paragraph
	element, <sgmltag>p</sgmltag>.</para>

      <example>
	<title><sgmltag>p</sgmltag></title>

	<para>Usage:</para>

	<programlisting><![CDATA[<p>This is a paragraph.  It can contain just about any
  other element.</p>]]></programlisting>
      </example>
    </sect2>

    <sect2 id="xhtml-markup-block-elements-block-quotations">
      <title>Block Quotations</title>

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

      <example>
	<title><sgmltag>blockquote</sgmltag></title>

	<para>Usage:</para>

	<programlisting><![CDATA[<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>]]></programlisting>
      </example>
    </sect2>

    <sect2 id="xhtml-markup-block-elements-lists">
      <title>Lists</title>

      <para><acronym>XHTML</acronym> can present the user with three
	types of lists: ordered, unordered, and definition.</para>

      <para>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.</para>

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

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

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

      <example>
	<title><sgmltag>ul</sgmltag> and
	  <sgmltag>ol</sgmltag></title>

	<para>Usage:</para>

	<programlisting><![CDATA[<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>]]></programlisting>
      </example>

      <example>
	<title>Definition Lists with <sgmltag>dl</sgmltag></title>

	<para>Usage:</para>

	<programlisting><![CDATA[<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>]]></programlisting>
      </example>
    </sect2>

    <sect2 id="xhtml-markup-block-elements-preformatted-text">
      <title>Pre-formatted Text</title>

      <para>Pre-formatted text can 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.</para>

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

      <example>
	<title><sgmltag>pre</sgmltag></title>

	<para>For example, the <sgmltag>pre</sgmltag> tags could be
	  used to mark up an email message:</para>

	<programlisting><![CDATA[<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>]]></programlisting>

	<para>Keep in mind that <literal>&lt;</literal> and
	  <literal>&amp;</literal> still are recognized as special
	  characters in pre-formatted text.  This is why the example
	  shown had to use <literal>&amp;lt;</literal> instead of
	  <literal>&lt;</literal>.  For consistency,
	  <literal>&amp;gt;</literal> was used in place of
	  <literal>&gt;</literal>, too.  Watch out for the special
	  characters that may appear in text copied from a plain-text
	  source, like an email message or program code.</para>
      </example>
    </sect2>

    <sect2 id="xhtml-markup-block-elements-tables">
      <title>Tables</title>

      <para>Mark up tabular information using the
	<sgmltag>table</sgmltag> element.  A table consists of one or
	more table rows (<sgmltag>tr</sgmltag>), each containing one
	or more cells of table data (<sgmltag>td</sgmltag>).  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 the <sgmltag>p</sgmltag>element is not needed.</para>

      <example>
	<title>Simple Use of <sgmltag>table</sgmltag></title>

	<para>Usage:</para>

	<programlisting><![CDATA[<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>]]></programlisting>
      </example>

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

      <example>
	<title>Using <literal>rowspan</literal></title>

	<para>Usage:</para>

	<programlisting><![CDATA[<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>]]></programlisting>
      </example>

      <example>
	<title>Using <literal>colspan</literal></title>

	<para>Usage:</para>

	<programlisting><![CDATA[<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>]]></programlisting>
      </example>

      <example>
	<title>Using <literal>rowspan</literal> and
	  <literal>colspan</literal> Together</title>

	<para>Usage:</para>

	<programlisting><![CDATA[<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>]]></programlisting>
      </example>
    </sect2>
  </sect1>

  <sect1 id="xhtml-markup-inline-elements">
    <title>In-line Elements</title>

    <sect2 id="xhtml-markup-inline-elements-emphasizing-information">
      <title>Emphasizing Information</title>

      <para>Two levels of emphasis are available in
	<acronym>XHTML</acronym>, <sgmltag>em</sgmltag> and
	<sgmltag>strong</sgmltag>. <sgmltag>em</sgmltag> is for a
	normal level of emphasis and <sgmltag>strong</sgmltag>
	indicates stronger emphasis.</para>

      <para>Typically, <sgmltag>em</sgmltag> is rendered in italic
	and <sgmltag>strong</sgmltag> is rendered in bold.  This is
	not always the case, however, and should not be relied upon.
	According to best practices, webpages only hold structural and
	semantical information and stylesheets are later applied to
	them.  Think of semantics, not formatting, when using these
	tags.</para>

      <example>
	<title><sgmltag>em</sgmltag> and
	  <sgmltag>strong</sgmltag></title>

	<para>Usage:</para>

	<programlisting><![CDATA[<p><em>This</em> has been emphasized, while
  <strong>this</strong> has been strongly emphasized.</p>]]></programlisting>
      </example>
    </sect2>

    <sect2 id="xhtml-markup-inline-elements-fixed-pitch-text">
      <title>Indicating Fixed-Pitch Text</title>

      <para>Content that should be rendered in a fixed pitch
	(typewriter) typeface is tagged with <sgmltag>tt</sgmltag>
	(for <quote>teletype</quote>).</para>

      <example>
	<title><sgmltag>tt</sgmltag></title>

	<para>Usage:</para>

	<programlisting><![CDATA[<p>This document was originally written by
  Nik Clayton, who can be reached by email as
  <tt>nik@FreeBSD.org</tt>.</p>]]></programlisting>
      </example>
    </sect2>

    <sect2 id="xhtml-markup-inline-elements-links">
      <title>Links</title>

      <note>
	<para>Links are also inline elements.</para>
      </note>

      <sect3 id="xhtml-markup-inline-elements-linking">
	<title>Linking to Other Documents on the Web</title>

	<para>A link points to the <acronym>URL</acronym> of another
	  document on the web.  The link is indicated with
	  <sgmltag>a</sgmltag>, and the <literal>href</literal>
	  attribute contains the <acronym>URL</acronym> of the target
	  document.  The content of the element becomes the link, and
	  is normally indicated to the user in some way,
	  typically by a different color or underlining.</para>

	<example>
	  <title>Using <literal>&lt;a href="..."&gt;</literal></title>

	  <para>Usage:</para>

	  <programlisting><![CDATA[<p>More information is available at the
  <a href="http://www.FreeBSD.org/">FreeBSD web site</a>.</p>]]></programlisting>
	</example>

	<para>These links will take the user to the top of the chosen
	  document.</para>
      </sect3>

      <sect3 id="xhtml-markup-inline-elements-other-parts">
	<title>Linking to Other Parts of Documents</title>

	<para>Linking to a point within another document, or within
	  the same document, requires that the document author include
	  <emphasis>anchors</emphasis>.  Anchors are indicated with
	  <sgmltag>a</sgmltag> and the <literal>id</literal> attribute
	  instead of <literal>href</literal>.</para>

	<example>
	  <title>Using <literal>&lt;a id="..."&gt;</literal></title>

	  <para>Usage:</para>

	  <programlisting><![CDATA[<p><a id="para1">This</a> paragraph can be referenced
  in other links with the name <tt>para1</tt>.</p>]]></programlisting>
	</example>

	<para>To link to a named part of a document, write a normal
	  link to that document, but include the <acronym>ID</acronym>
	  of the anchor after a <literal>#</literal> symbol.</para>

	<example>
	  <title>Linking to a Named Part of Another Document</title>

	  <para>Assume that the <literal>para1</literal> example
	    resides in a document called
	    <filename>foo.html</filename>.</para>

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

	<para>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
	  <literal>#</literal>).</para>

	<example>
	  <title>Linking to a Named Part of the Same Document</title>

	  <para>Assume that the <literal>para1</literal> example
	    resides in this document:</para>

	  <programlisting><![CDATA[<p>More information can be found in the
  <a href="#para1">first paragraph</a> of this
  document.</p>]]></programlisting>
	</example>
      </sect3>
    </sect2>
  </sect1>
</chapter>