xhtml1.xhtml

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entity for the Euro currency sign (<code>&amp;euro;</code> or
<code>&amp;#8364;</code> or <code>&amp;#x20AC;</code>) is defined
as part of the special characters.</p>

<ul>
<li>
<p><a href="DTD/xhtml-lat1.ent">Latin-1 characters</a></p>
</li>

<li>
<p><a href="DTD/xhtml-special.ent">Special characters</a></p>
</li>

<li>
<p><a href="DTD/xhtml-symbol.ent">Symbols</a></p>
</li>
</ul>

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<h1><a name="prohibitions" id="prohibitions">Appendix B. Element
Prohibitions</a></h1>

<p><b>This appendix is normative.</b></p>

<p>The following elements have prohibitions on which elements
they can contain (see <a href="#h-4.9">Section 4.9</a>). This
prohibition applies to all depths of nesting, i.e. it contains
all the descendant elements.</p>

<dl><dt><code class="tag">a</code></dt>
<dd>
cannot contain other <code>a</code> elements.</dd>
<dt><code class="tag">pre</code></dt>
<dd>cannot contain the <code>img</code>, <code>object</code>,
<code>big</code>, <code>small</code>, <code>sub</code>, or <code>
sup</code> elements.</dd>

<dt><code class="tag">button</code></dt>
<dd>cannot contain the <code>input</code>, <code>select</code>,
<code>textarea</code>, <code>label</code>, <code>button</code>,
<code>form</code>, <code>fieldset</code>, <code>iframe</code> or
<code>isindex</code> elements.</dd>
<dt><code class="tag">label</code></dt>
<dd>cannot contain other <code class="tag">label</code> elements.</dd>
<dt><code class="tag">form</code></dt>
<dd>cannot contain other <code>form</code> elements.</dd>
</dl>

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<h1><a name="guidelines" id="guidelines">Appendix C.
HTML Compatibility Guidelines</a></h1>

<p><b>This appendix is informative.</b></p>

<p>This appendix summarizes design guidelines for authors who
wish their XHTML documents to render on existing HTML user
agents.</p>

<h2>C.1 Processing Instructions</h2>
<p>Be aware that processing instructions are rendered on some
user agents. However, also note that when the XML declaration is not included
in a document, the document can only use the default character encodings UTF-8
or UTF-16.</p>

<h2>C.2 Empty Elements</h2>
<p>Include a space before the trailing <code>/</code> and <code>
&gt;</code> of empty elements, e.g. <code class="greenmono">
&lt;br&#160;/&gt;</code>, <code class="greenmono">
&lt;hr&#160;/&gt;</code> and <code class="greenmono">&lt;img
src="karen.jpg" alt="Karen"&#160;/&gt;</code>. Also, use the
minimized tag syntax for empty elements, e.g. <code class= 
"greenmono">&lt;br /&gt;</code>, as the alternative syntax <code
class="greenmono">&lt;br&gt;&lt;/br&gt;</code> allowed by XML
gives uncertain results in many existing user agents.</p>

<h2>C.3 Element Minimization and Empty Element Content</h2>
<p>Given an empty instance of an element whose content model is
not <code>EMPTY</code> (for example, an empty title or paragraph)
do not use the minimized form (e.g. use <code class="greenmono">
&lt;p&gt; &lt;/p&gt;</code> and not <code class="greenmono">
&lt;p&#160;/&gt;</code>).</p>

<h2>C.4 Embedded Style Sheets and Scripts</h2>
<p>Use external style sheets if your style sheet uses <code>
&lt;</code> or <code>&amp;</code> or <code>]]&gt;</code> or <code>--</code>. Use
external scripts if your script uses <code>&lt;</code> or <code>
&amp;</code> or <code>]]&gt;</code> or <code>--</code>. Note that XML parsers
are permitted to silently remove the contents of comments. Therefore, the historical
practice of "hiding" scripts and style sheets within comments to make the
documents backward compatible is likely to not work as expected in XML-based
implementations.</p>

<h2>C.5 Line Breaks within Attribute Values</h2>
<p>Avoid line breaks and multiple whitespace characters within
attribute values. These are handled inconsistently by user
agents.</p>

<h2>C.6 Isindex</h2>
<p>Don't include more than one <code>isindex</code> element in
the document <code>head</code>. The <code>isindex</code> element
is deprecated in favor of the <code>input</code> element.</p>

<h2>C.7 The <code>lang</code> and <code>xml:lang</code> Attributes</h2>
<p>Use both the <code>lang</code> and <code>xml:lang</code>
attributes when specifying the language of an element. The value
of the <code>xml:lang</code> attribute takes precedence.</p>

<h2>C.8 Fragment Identifiers</h2>
<p>In XML, <abbr title="Uniform Resource Identifiers">URIs</abbr> [<a href="#ref-rfc2396">RFC2396</a>] that end with fragment identifiers of the form
<code>"#foo"</code> do not refer to elements with an attribute
<code>name="foo"</code>; rather, they refer to elements with an
attribute defined to be of type <code>ID</code>, e.g., the <code>
id</code> attribute in HTML 4.0. Many existing HTML clients don't
support the use of <code>ID</code>-type attributes in this way,
so identical values may be supplied for both of these attributes to ensure
maximum forward and backward compatibility (e.g., <code class= 
"greenmono">&lt;a id="foo" name="foo"&gt;...&lt;/a&gt;</code>).</p>

<p>Further, since the set of
legal values for attributes of type <code>ID</code> is much smaller than
for those of type <code>CDATA</code>, the type of the <code>name</code>
attribute has been changed to <code>NMTOKEN</code>. This attribute is 
constrained such that it can only have the same values as type
<code>ID</code>, or as the <code>Name</code> production in XML 1.0 Section
2.5, production 5. Unfortunately, this constraint cannot be expressed in the
XHTML 1.0 DTDs.  Because of this change, care must be taken when
converting existing HTML documents. The values of these attributes
must be unique within the document, valid, and any references to these 
fragment identifiers (both
internal and external) must be updated should the values be changed during
conversion.</p>
<p>Finally, note that XHTML 1.0 has deprecated the
<code>name</code> attribute of the <code>a</code>, <code>applet</code>, <code>frame</code>, <code>iframe</code>, <code>img</code>, and <code>map</code>
elements, and it will be
removed from XHTML in subsequent versions.</p>

<h2>C.9 Character Encoding</h2>
<p>To specify a character encoding in the document, use both the
encoding attribute specification on the xml declaration (e.g.
<code class="greenmono">&lt;?xml version="1.0"
encoding="EUC-JP"?&gt;</code>) and a meta http-equiv statement
(e.g. <code class="greenmono">&lt;meta http-equiv="Content-type"
content='text/html; charset="EUC-JP"'&#160;/&gt;</code>). The
value of the encoding attribute of the xml processing instruction
takes precedence.</p>

<h2>C.10 Boolean Attributes</h2>
<p>Some HTML user agents are unable to interpret boolean
attributes when these appear in their full (non-minimized) form,
as required by XML 1.0. Note this problem doesn't effect user
agents compliant with HTML 4.0. The following attributes are
involved: <code>compact</code>, <code>nowrap</code>, <code>
ismap</code>, <code>declare</code>, <code>noshade</code>, <code>
checked</code>, <code>disabled</code>, <code>readonly</code>,
<code>multiple</code>, <code>selected</code>, <code>
noresize</code>, <code>defer</code>.</p>

<h2>C.11 Document Object Model and XHTML</h2>
<p>
The Document Object Model level 1 Recommendation [<a href="#ref-dom">DOM</a>]
defines document object model interfaces for XML and HTML 4.0. The HTML 4.0
document object model specifies that HTML element and attribute names are
returned in upper-case. The XML document object model specifies that 
element and attribute names are returned in the case they are specified. In
XHTML 1.0, elements and attributes are specified in lower-case. This apparent difference can be
addressed in two ways:
</p>
<ol>
<li>Applications that access XHTML documents served as Internet media type
<code>text/html</code>
via the <abbr title="Document Object Model">DOM</abbr> can use the HTML DOM,
and can rely upon element and attribute names being returned in
upper-case from those interfaces.</li>
<li>Applications that access XHTML documents served as Internet media types
<code>text/xml</code> or <code>application/xml</code>
can also use the XML DOM. Elements and attributes will be returned in lower-case.
Also, some XHTML elements may or may
not appear
in the object tree because they are optional in the content model
(e.g. the <code>tbody</code> element within
<code>table</code>).  This occurs because in HTML 4.0 some elements were
permitted to be minimized such that their start and end tags are both omitted
(an SGML feature).
This is not possible in XML. Rather than require document authors to insert
extraneous elements, XHTML has made the elements optional. 
Applications need to adapt to this
accordingly.</li>
</ol>

<h2>C.12 Using Ampersands in Attribute Values</h2>
<p>
When an attribute value contains an ampersand, it must be expressed as a character
entity reference
(e.g. "<code>&amp;amp;</code>"). For example, when the
<code>href</code> attribute
of the <code>a</code> element refers to a
CGI script that takes parameters, it must be expressed as
<code>http://my.site.dom/cgi-bin/myscript.pl?class=guest&amp;amp;name=user</code>
rather than as
<code>http://my.site.dom/cgi-bin/myscript.pl?class=guest&amp;name=user</code>.
</p>

<h2>C.13 Cascading Style Sheets (CSS) and XHTML</h2>

<p>The Cascading Style Sheets level 2 Recommendation [<a href="#ref-css2">CSS2</a>] defines style
properties which are applied to the parse tree of the HTML or XML
document.  Differences in parsing will produce different visual or
aural results, depending on the selectors used. The following hints
will reduce this effect for documents which are served without
modification as both media types:</p>

<ol>
<li>
CSS style sheets for XHTML should use lower case element and
attribute names.</li>


<li>In tables, the tbody element will be inferred by the parser of an
HTML user agent, but not by the parser of an XML user agent. Therefore
you should always explicitely add a tbody element if it is referred to
in a CSS selector.</li>

<li>Within the XHTML name space, user agents are expected to
recognize the "id" attribute as an attribute of type ID.
Therefore, style sheets should be able to continue using the
shorthand "#" selector syntax even if the user agent does not read
the DTD.</li>

<li>Within the XHTML name space, user agents are expected to
recognize the "class" attribute. Therefore, style sheets should be
able to continue using the shorthand "." selector syntax.</li>

<li>
CSS defines different conformance rules for HTML and XML documents;
be aware that the HTML rules apply to XHTML documents delivered as
HTML and the XML rules apply to XHTML documents delivered as XML.</li>
</ol>
<!--OddPage-->
<h1><a name="acks" id="acks">Appendix D.
Acknowledgements</a></h1>

<p><b>This appendix is informative.</b></p>

<p>This specification was written with the participation of the
members of the W3C HTML working group:</p>

<dl>
<dd>Steven Pemberton, CWI (HTML Working Group Chair)<br />
Murray Altheim, Sun Microsystems<br />
Daniel Austin, CNET: The Computer Network<br />
Frank Boumphrey, HTML Writers Guild<br />
John Burger, Mitre<br />
Andrew W. Donoho, IBM<br />
Sam Dooley, IBM<br />
Klaus Hofrichter, GMD<br />
Philipp Hoschka, W3C<br />
Masayasu Ishikawa, W3C<br />
Warner ten Kate, Philips Electronics<br />
Peter King, Phone.com<br />
Paula Klante, JetForm<br />
Shin'ichi Matsui, W3C/Panasonic<br />
Shane McCarron, Applied Testing and Technology (The Open Group through August
1999)<br />
Ann Navarro, HTML Writers Guild<br />
Zach Nies, Quark<br />
Dave Raggett, W3C/HP (W3C lead for HTML)<br />
Patrick Schmitz, Microsoft<br />
Sebastian Schnitzenbaumer, Stack Overflow<br />
Chris Wilson, Microsoft<br />
Ted Wugofski, Gateway 2000<br />
Dan Zigmond, WebTV Networks</dd>
</dl>

<!--OddPage-->
<h1><a name="refs" id="refs">Appendix E. References</a></h1>

<p><b>This appendix is informative.</b></p>

<dl>

<dt><a name="ref-css2" id="ref-css2"><b>[CSS2]</b></a></dt>

<dd><a href="http://www.w3.org/TR/REC-CSS2">"Cascading Style Sheets, level 2 (CSS2) Specification"</a>, B.
Bos, H. W. Lie, C. Lilley, I. Jacobs, 12 May 1998.<br />
Available at: <a href="http://www.w3.org/TR/REC-CSS2">
http://www.w3.org/TR/REC-CSS2</a></dd>

<dt><a name="ref-dom" id="ref-dom"><b>[DOM]</b></a></dt>

<dd><a href="http://www.w3.org/TR/REC-DOM-Level-1">"Document Object Model (DOM) Level 1 Specification"</a>, Lauren
Wood <i>et al.</i>, 1 October 1998.<br />
Available at: <a href="http://www.w3.org/TR/REC-DOM-Level-1">
http://www.w3.org/TR/REC-DOM-Level-1</a></dd>

<dt><a name="ref-html4" id="ref-html4"><b>[HTML]</b></a></dt>

<dd><a href="http://www.w3.org/TR/1999/PR-html40-19990824">"HTML 4.01 Specification"</a>, D. Raggett, A. Le&#160;Hors, I.
Jacobs, 24 August 1999.<br />
Available at: <a href="http://www.w3.org/TR/1999/PR-html40-19990824">
http://www.w3.org/TR/1999/PR-html40-19990824</a></dd>

<dt><a name="ref-posix" id="ref-posix"><b>[POSIX.1]</b></a></dt>

<dd>"ISO/IEC 9945-1:1990 Information Technology - Portable
Operating System Interface (POSIX) - Part 1: System Application
Program Interface (API) [C Language]", Institute of Electrical
and Electronics Engineers, Inc, 1990.</dd>

<dt><a name="ref-rfc2046" id="ref-rfc2046"><b>
[RFC2046]</b></a></dt>

<dd><a href="http://www.ietf.org/rfc/rfc2046.txt">"RFC2046: Multipurpose Internet Mail Extensions (MIME) Part
Two: Media Types"</a>, N. Freed and N. Borenstein, November
1996.<br />
Available at <a href="http://www.ietf.org/rfc/rfc2046.txt">
http://www.ietf.org/rfc/rfc2046.txt</a>. Note that this RFC
obsoletes RFC1521, RFC1522, and RFC1590.</dd>

<dt><a name="ref-rfc2119" id="ref-rfc2119"><b>
[RFC2119]</b></a></dt>

<dd><a href="http://www.ietf.org/rfc/rfc2119.txt">"RFC2119: Key words for use in RFCs to Indicate Requirement
Levels"</a>, S. Bradner, March 1997.<br />
Available at: <a href="http://www.ietf.org/rfc/rfc2119.txt">
http://www.ietf.org/rfc/rfc2119.txt</a></dd>

<dt><a name="ref-rfc2376" id="ref-rfc2376"><b>
[RFC2376]</b></a></dt>

<dd><a href="http://www.ietf.org/rfc/rfc2376.txt">"RFC2376: XML Media Types"</a>, E. Whitehead, M. Murata, July
1998.<br />
Available at: <a href="http://www.ietf.org/rfc/rfc2376.txt">
http://www.ietf.org/rfc/rfc2376.txt</a></dd>

<dt><a name="ref-rfc2396" id="ref-rfc2396"><b>
[RFC2396]</b></a></dt>

<dd><a href="http://www.ietf.org/rfc/rfc2396.txt">"RFC2396: Uniform Resource Identifiers (URI): Generic
Syntax"</a>, T. Berners-Lee, R. Fielding, L. Masinter, August
1998.<br />
This document updates RFC1738 and RFC1808.<br />
Available at: <a href="http://www.ietf.org/rfc/rfc2396.txt">
http://www.ietf.org/rfc/rfc2396.txt</a></dd>

<dt><a name="ref-xml" id="ref-xml"><b>[XML]</b></a></dt>

<dd><a href="http://www.w3.org/TR/REC-xml">"Extensible Markup Language (XML) 1.0 Specification"</a>, T.
Bray, J. Paoli, C. M. Sperberg-McQueen, 10 February 1998.<br />
Available at: <a href="http://www.w3.org/TR/REC-xml">
http://www.w3.org/TR/REC-xml</a></dd>

<dt><a name="ref-xmlns" id="ref-xmlns"><b>[XMLNAMES]</b></a></dt>

<dd><a href="http://www.w3.org/TR/REC-xml-names">"Namespaces in XML"</a>, T. Bray, D. Hollander, A. Layman, 14
January 1999.<br />
XML namespaces provide a simple method for qualifying names used
in XML documents by associating them with namespaces identified
by URI.<br />
Available at: <a href="http://www.w3.org/TR/REC-xml-names">
http://www.w3.org/TR/REC-xml-names</a></dd>

</dl>
<p><a href="http://www.w3.org/WAI/WCAG1AAA-Conformance"
title="Explanation of Level Triple-A Conformance">
<img height="32" width="88" 
src="wcag1AAA.gif"
alt="Level Triple-A conformance icon, W3C-WAI Web Content Accessibility Guidelines 1.0" /></a></p>
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