xhtml1.xhtml

下载来的一个看图软件的源代码

<ul>
<li>
All whitespace surrounding block elements should be removed.
</li>
<li>
Comments are removed entirely and do not affect whitespace handling. One
whitespace character on either side of a comment is treated as two white
space characters.
</li>
<li>
Leading and trailing whitespace inside a block element must be removed.
</li>
<li>Line feed characters within a block element must be converted into a
space (except when the 'xml:space' attribute is set to 'preserve').
</li>
<li>
A sequence of white space characters must be reduced to a single space
character (except when the 'xml:space' attribute is set to 'preserve').
</li>
<li>
With regard to rendition,
the User Agent should render the content in a
manner appropriate to the language in which the content is written.
In languages whose primary script is Latinate, the ASCII space
character is typically used to encode both grammatical word boundaries and
typographic whitespace; in languages whose script is related to Nagari
(e.g., Sanskrit, Thai, etc.), grammatical boundaries may be encoded using
the ZW 'space' character, but will not typically be represented by
typographic whitespace in rendered output; languages using Arabiform scripts
may encode typographic whitespace using a space character, but may also use
the ZW space character to delimit 'internal' grammatical boundaries (what
look like words in Arabic to an English eye frequently encode several words,
e.g. 'kitAbuhum' = 'kitAbu-hum' = 'book them' == their book); and languages
in the Chinese script tradition typically neither encode such delimiters nor
use typographic whitespace in this way. 
</li>
</ul>

<p>Whitespace in attribute values is processed according to <a
href="#ref-xml">[XML]</a>.</p>
</li>
</ol>

<!--OddPage-->
<h1><a name="diffs" id="diffs">4. Differences with HTML
4.0</a></h1>

<p>Due to the fact that XHTML is an XML application, certain
practices that were perfectly legal in SGML-based HTML 4.0 <a
href="#ref-html4">[HTML]</a> must be changed.</p>

<h2><a name="h-4.1" id="h-4.1">4.1 Documents must be
well-formed</a></h2>

<p><a href="#wellformed">Well-formedness</a> is a new concept
introduced by <a href="#ref-xml">[XML]</a>. Essentially this
means that all elements must either have closing tags or be
written in a special form (as described below), and that all the
elements must nest.</p>

<p>Although overlapping is illegal in SGML, it was widely
tolerated in existing browsers.</p>

<div class="good">
<p><strong><em>CORRECT: nested elements.</em></strong></p>

<p>&lt;p&gt;here is an emphasized
&lt;em&gt;paragraph&lt;/em&gt;.&lt;/p&gt;</p>
</div>

<div class="bad">
<p><strong><em>INCORRECT: overlapping elements</em></strong></p>

<p>&lt;p&gt;here is an emphasized
&lt;em&gt;paragraph.&lt;/p&gt;&lt;/em&gt;</p>
</div>

<h2><a name="h-4.2" id="h-4.2">4.2 Element and attribute
names must be in lower case</a></h2>

<p>XHTML documents must use lower case for all HTML element and
attribute names. This difference is necessary because XML is
case-sensitive e.g. &lt;li&gt; and &lt;LI&gt; are different
tags.</p>

<h2><a name="h-4.3" id="h-4.3">4.3 For non-empty elements,
end tags are required</a></h2>

<p>In SGML-based HTML 4.0 certain elements were permitted to omit
the end tag; with the elements that followed implying closure.
This omission is not permitted in XML-based XHTML. All elements
other than those declared in the DTD as <code>EMPTY</code> must
have an end tag.</p>

<div class="good">
<p><strong><em>CORRECT: terminated elements</em></strong></p>

<p>&lt;p&gt;here is a paragraph.&lt;/p&gt;&lt;p&gt;here is
another paragraph.&lt;/p&gt;</p>
</div>

<div class="bad">
<p><strong><em>INCORRECT: unterminated elements</em></strong></p>

<p>&lt;p&gt;here is a paragraph.&lt;p&gt;here is another
paragraph.</p>
</div>

<h2><a name="h-4.4" id="h-4.4">4.4 Attribute values must
always be quoted</a></h2>

<p>All attribute values must be quoted, even those which appear
to be numeric.</p>

<div class="good">
<p><strong><em>CORRECT: quoted attribute values</em></strong></p>

<p>&lt;table rows="3"&gt;</p>
</div>

<div class="bad">
<p><strong><em>INCORRECT: unquoted attribute values</em></strong></p>

<p>&lt;table rows=3&gt;</p>
</div>

<h2><a name="h-4.5" id="h-4.5">4.5 Attribute
Minimization</a></h2>

<p>XML does not support attribute minimization. Attribute-value
pairs must be written in full. Attribute names such as <code>
compact</code> and <code>checked</code> cannot occur in elements
without their value being specified.</p>

<div class="good">
<p><strong><em>CORRECT: unminimized attributes</em></strong></p>

<p>&lt;dl compact="compact"&gt;</p>
</div>

<div class="bad">
<p><strong><em>INCORRECT: minimized attributes</em></strong></p>

<p>&lt;dl compact&gt;</p>
</div>

<h2><a name="h-4.6" id="h-4.6">4.6 Empty Elements</a></h2>

<p>Empty elements must either have an end tag or the start tag must end with <code>/&gt;</code>. For instance,
<code>&lt;br/&gt;</code> or <code>&lt;hr&gt;&lt;/hr&gt;</code>. See <a
href="#guidelines">HTML Compatibility Guidelines</a> for information on ways to
ensure this is backward compatible with HTML 4.0 user agents.</p>

<div class="good">
<p><strong><em>CORRECT: terminated empty tags</em></strong></p>

<p>&lt;br/&gt;&lt;hr/&gt;</p>
</div>

<div class="bad">
<p><strong><em>INCORRECT: unterminated empty tags</em></strong></p>

<p>&lt;br&gt;&lt;hr&gt;</p>
</div>

<h2><a name="h-4.7" id="h-4.7">4.7 Whitespace handling in
attribute values</a></h2>

<p>In attribute values, user agents will strip leading and
trailing whitespace from attribute values and map sequences
of one or more whitespace characters (including line breaks) to
a single inter-word space (an ASCII space character for western
scripts). See <a href="http://www.w3.org/TR/REC-xml#AVNormalize">
Section 3.3.3</a> of <a href="#ref-xml">[XML]</a>.</p>

<h2><a name="h-4.8" id="h-4.8">4.8 Script and Style
elements</a></h2>

<p>In XHTML, the script and style elements are declared as having
<code>#PCDATA</code> content. As a result, <code>&lt;</code> and
<code>&amp;</code> will be treated as the start of markup, and
entities such as <code>&amp;lt;</code> and <code>&amp;amp;</code>
will be recognized as entity references by the XML processor to
<code>&lt;</code> and <code>&amp;</code> respectively. Wrapping
the content of the script or style element within a <code>
CDATA</code> marked section avoids the expansion of these
entities.</p>

<div class="good">
<pre>
&lt;script&gt;
 &lt;![CDATA[
 ... unescaped script content ...
 ]]&gt;
 &lt;/script&gt;
</pre>
</div>

<p><code>CDATA</code> sections are recognized by the XML
processor and appear as nodes in the Document Object Model, see
<a href= 
"http://www.w3.org/TR/REC-DOM-Level-1/level-one-core.html#ID-E067D597">
Section 1.3</a> of the DOM Level 1 Recommendation <a href= 
"#ref-dom">[DOM]</a>.</p>

<p>An alternative is to use external script and style
documents.</p>

<h2><a name="h-4.9" id="h-4.9">4.9 SGML exclusions</a></h2>

<p>SGML gives the writer of a DTD the ability to exclude specific
elements from being contained within an element. Such
prohibitions (called "exclusions") are not possible in XML.</p>

<p>For example, the HTML 4.0 Strict DTD forbids the nesting of an
'<code>a</code>' element within another '<code>a</code>' element
to any descendant depth. It is not possible to spell out such
prohibitions in XML. Even though these prohibitions cannot be
defined in the DTD, certain elements should not be nested. A
summary of such elements and the elements that should not be
nested in them is found in the normative <a href="#prohibitions">
Appendix&#160;B</a>.</p>

<h2><a name="h-4.10" id="h-4.10">4.10 The elements with 'id' and 'name'
attributes</a></h2>

<p>HTML 4.0 defined the <code>name</code> attribute for the elements
<code>a</code>,
<code>applet</code>, <code>frame</code>,
<code>iframe</code>, <code>img</code>, and <code>map</code>.
HTML 4.0 also introduced
the <code>id</code> attribute. Both of these attributes are designed to be
used as fragment identifiers.</p>
<p>In XML, fragment identifiers are of type <code>ID</code>, and
there can only be a single attribute of type <code>ID</code> per element.
Therefore, in XHTML 1.0 the <code>id</code>
attribute is defined to be of type <code>ID</code>. In order to
ensure that XHTML 1.0 documents are well-structured XML documents, XHTML 1.0
documents MUST use the <code>id</code> attribute when defining fragment
identifiers, even on elements that historically have also had a
<code>name</code> attribute.
See the <a href="#guidelines">HTML Compatibility
Guidelines</a> for information on ensuring such anchors are backwards
compatible when serving XHTML documents as media type <code>text/html</code>.
</p>
<p>Note that in XHTML 1.0, the <code>name</code> attribute of these
elements is formally deprecated, and will be removed in a
subsequent version of XHTML.</p>

<!--OddPage-->
<h1><a name="issues" id="issues">5. Compatibility Issues</a></h1>

<p>Although there is no requirement for XHTML 1.0 documents to be
compatible with existing user agents, in practice this is easy to
accomplish. Guidelines for creating compatible documents can be
found in <a href="#guidelines">Appendix&#160;C</a>.</p>

<h2><a name="media" id="media">5.1 Internet Media Type</a></h2>
<p>As of the publication of this recommendation, the general
recommended MIME labeling for XML-based applications
has yet to be resolved.</p>

<p>However, XHTML Documents which follow the guidelines set forth
in <a href="#guidelines">Appendix C</a>, "HTML Compatibility Guidelines" may be
labeled with the Internet Media Type "text/html", as they
are compatible with most HTML browsers. This document
makes no recommendation about MIME labeling of other
XHTML documents.</p>

<!--OddPage-->
<h1><a name="future" id="future">6. Future Directions</a></h1>

<p>XHTML 1.0 provides the basis for a family of document types
that will extend and subset XHTML, in order to support a wide
range of new devices and applications, by defining modules and
specifying a mechanism for combining these modules. This
mechanism will enable the extension and sub-setting of XHTML 1.0
in a uniform way through the definition of new modules.</p>

<h2><a name="mods" id="mods">6.1 Modularizing HTML</a></h2>

<p>As the use of XHTML moves from the traditional desktop user
agents to other platforms, it is clear that not all of the XHTML
elements will be required on all platforms. For example a hand
held device or a cell-phone may only support a subset of XHTML
elements.</p>

<p>The process of modularization breaks XHTML up into a series of
smaller element sets. These elements can then be recombined to
meet the needs of different communities.</p>

<p>These modules will be defined in a later W3C document.</p>

<h2><a name="extensions" id="extensions">6.2 Subsets and
Extensibility</a></h2>

<p>Modularization brings with it several advantages:</p>

<ul>
<li>
<p>It provides a formal mechanism for sub-setting XHTML.</p>
</li>

<li>
<p>It provides a formal mechanism for extending XHTML.</p>
</li>

<li>
<p>It simplifies the transformation between document types.</p>
</li>

<li>
<p>It promotes the reuse of modules in new document types.</p>
</li>
</ul>

<h2><a name="profiles" id="profiles">6.3 Document
Profiles</a></h2>

<p>A document profile specifies the syntax and semantics of a set
of documents. Conformance to a document profile provides a basis
for interoperability guarantees. The document profile specifies
the facilities required to process documents of that type, e.g.
which image formats can be used, levels of scripting, style sheet
support, and so on.</p>

<p>For product designers this enables various groups to define
their own standard profile.</p>

<p>For authors this will obviate the need to write several
different versions of documents for different clients.</p>

<p>For special groups such as chemists, medical doctors, or
mathematicians this allows a special profile to be built using
standard HTML elements plus a group of elements geared to the
specialist's needs.</p>

<!--OddPage-->
<h1><a name="appendices" id="appendices"></a>
<a name="dtds" id="dtds">Appendix A. DTDs</a></h1>

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

<p>These DTDs and entity sets form a normative part of this
specification. The complete set of DTD files together with an XML
declaration and SGML Open Catalog is included in the <a href= 
"xhtml1.zip">zip file</a> for this specification.</p>

<h2><a name="h-A1" id="h-A1">A.1 Document Type
Definitions</a></h2>

<p>These DTDs approximate the HTML 4.0 DTDs. It is likely that
when the DTDs are modularized, a method of DTD construction will
be employed that corresponds more closely to HTML 4.0.</p>

<ul>
<li>
<p><a href="DTD/xhtml1-strict.dtd" type="text/plain">
XHTML-1.0-Strict</a></p>
</li>

<li>
<p><a href="DTD/xhtml1-transitional.dtd" type="text/plain">
XHTML-1.0-Transitional</a></p>
</li>

<li>
<p><a href="DTD/xhtml1-frameset.dtd" type="text/plain">
XHTML-1.0-Frameset</a></p>
</li>
</ul>

<h2><a name="h-A2" id="h-A2">A.2 Entity Sets</a></h2>

<p>The XHTML entity sets are the same as for HTML 4.0, but have
been modified to be valid XML 1.0 entity declarations. Note the