Many (X)HTML tags are obscure and rarely used, or used incorrectly.
Proper use of markup gives documents richer semantic meaning.
<table...> tag
<table
summary="Table 23. Ability of W3C markup
specifications to create well-formed XML markup."
>
<tr>
<th colspan="3" id="property">Valid XML?</th>
...
</tr>
...
<caption...> tag nested in the <table...> tag
<table ...>
<caption>
Table 23. Ability of W3C markup specifications to
create well-formed XML markup.
</caption>
<tr>
<th colspan="3" id="property">Valid XML?</th>
...
</tr>
...
<tr>
<th id="html401">HTML 4.01Transtitional</th>
<th id="xhtmltrans">XHTML 1.0 Transitional</th>
<th id="htmlstrict">XHTML 1.0 Strict</th>
</tr>
<tr>
<td headers="html401">No</td>
<td headers="xhtmltrans"">Yes</td>
<td headers="xhtmlstrict">Yes</td>
</tr>
<sup class="footnote">
<a id="footnote-3-referrer" href="#footnote-3">[3]</a>
</sup>
<h2>Footnotes<h2>
<ul>
<li>><a id="footnote-3" href="#footnote-3-referrer">[3]</a>
Content of footnote.</li>
</ul>
Example document with footnotes
<head>
<title>Metadata in Web Pages</title>
<link rel="stylesheet" type="text/css"
href="styles.css" />
</head>
<html xmlns:DC="http://purl.org/dc/elements/1.1/">
<head>
<meta http-equiv="Content-type"
content="text/html; charset=utf-8" />
<meta http-equiv="Content-Language" content="en-us" />
<meta name="DC.title"
content="Metadata: Unused and Unloved" />
<meta name="DC.description" content="Metadata: Improve
usability with metdata." />
<meta name="DC.rights"
content="Copyright (c)2005 Christian Johansen" />
...
</head>
<body>)
...
<h3>Roll Roll Roll</h3>
<ul>
...
<li><a href="http://koreacrunch.com/"
rel="contact colleague">Channy Young</a></li>
<li><a href="http://superfluousbanter.org/"
rel="friend met colleague">Dan Rubin</a></li>
...
</ul>
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:wairole="http://www.w3.org/2005/01/wai-rdf/GUIRoleTaxonomy#"
>
<body>
<div role="navigation">
<ul>
<li> <a href="www.w3.org/WAI">WAI</a></li>
<li> <a href="www.ibm.com/able">IBM Accessibility ...</a></li>
<li> <a href="www.opera.com">Opera Software</a></li>
<li><a href="www.mozilla.org/access">Mozilla ...</a></li>
<li><a href="www.ubaccess.com">UB Access</a></li>
</ul>
...
http://tinyurl.com/2rs946