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diff --git a/xhtml1-20020801/diffs.html b/xhtml1-20020801/diffs.html new file mode 100644 index 0000000..c65627d --- /dev/null +++ b/xhtml1-20020801/diffs.html @@ -0,0 +1,211 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" +"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> +<html lang="en" xml:lang="en" xmlns="http://www.w3.org/1999/xhtml"> +<head> +<meta name="generator" content="HTML Tidy, see www.w3.org" /> +<title>XHTML 1.0 - Differences with HTML 4</title> +<link rel="stylesheet" type="text/css" media="screen" href="xhtml.css" /> +<link rel="stylesheet" type="text/css" media="screen" href="W3C-REC.css" /> +</head> +<body> +<div class="navbar">[<a href="normative.html">previous</a>]   [<a href="issues.html">next</a>]   [<a href="Cover.html#toc">table of contents</a>] + +<hr /> +</div> + +<h1><a name="diffs" id="diffs">4.</a> Differences with HTML 4</h1> + +<div class='subtoc'> +<p><strong>Contents</strong></p> + +<ul class='toc'> +<li class='tocline'>4.1. <a href="#h-4.1" class="tocxref">Documents must be well-formed</a></li> + +<li class='tocline'>4.2. <a href="#h-4.2" class="tocxref">Element and attribute names must be in lower case</a></li> + +<li class='tocline'>4.3. <a href="#h-4.3" class="tocxref">For non-empty elements, end tags are required</a></li> + +<li class='tocline'>4.4. <a href="#h-4.4" class="tocxref">Attribute values must always be quoted</a></li> + +<li class='tocline'>4.5. <a href="#h-4.5" class="tocxref">Attribute Minimization</a></li> + +<li class='tocline'>4.6. <a href="#h-4.6" class="tocxref">Empty Elements</a></li> + +<li class='tocline'>4.7. <a href="#h-4.7" class="tocxref">White Space handling in attribute values</a></li> + +<li class='tocline'>4.8. <a href="#h-4.8" class="tocxref">Script and Style elements</a></li> + +<li class='tocline'>4.9. <a href="#h-4.9" class="tocxref">SGML exclusions</a></li> + +<li class='tocline'>4.10. <a href="#h-4.10" class="tocxref">The elements with 'id' and 'name' attributes</a></li> + +<li class='tocline'>4.11. <a href="#h-4.11" class="tocxref">Attributes with pre-defined value sets</a></li> + +<li class='tocline'>4.12. <a href="#h-4.12" class="tocxref">Entity references as hex values</a></li> +</ul> +</div> + +<p><strong>This section is informative.</strong></p> + +<p>Due to the fact that XHTML is an XML application, certain practices that were perfectly legal in SGML-based HTML 4 [<a class="nref" href="references.html#ref-html4">HTML4</a>] must be +changed.</p> + +<h2><a name="h-4.1" id="h-4.1">4.1.</a> Documents must be well-formed</h2> + +<p><a href="definitions.html#wellformed">Well-formedness</a> is a new concept introduced by [<a class="nref" href="references.html#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 properly.</p> + +<p>Although overlapping is illegal in SGML, it is widely tolerated in existing browsers.</p> + +<p><strong><em>CORRECT: nested elements.</em></strong></p> + +<div class="good"> +<p><p>here is an emphasized <em>paragraph</em>.</p></p> +</div> + +<p><strong><em>INCORRECT: overlapping elements</em></strong></p> + +<div class="bad"> +<p><p>here is an emphasized <em>paragraph.</p></em></p> +</div> + +<h2><a name="h-4.2" id="h-4.2">4.2.</a> Element and attribute names must be in lower case</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. <li> and <LI> are different tags.</p> + +<h2><a name="h-4.3" id="h-4.3">4.3.</a> For non-empty elements, end tags are required</h2> + +<p>In SGML-based HTML 4 certain elements were permitted to omit the end tag; with the elements that followed implying closure. XML does not allow end tags to be omitted. All elements other than those +declared in the DTD as <code>EMPTY</code> must have an end tag. Elements that are declared in the DTD as <code>EMPTY</code> can have an end tag <em>or</em> can use empty element shorthand (see <a +href="#h-4.6">Empty Elements</a>).</p> + +<p><strong><em>CORRECT: terminated elements</em></strong></p> + +<div class="good"> +<p><p>here is a paragraph.</p><p>here is another paragraph.</p></p> +</div> + +<p><strong><em>INCORRECT: unterminated elements</em></strong></p> + +<div class="bad"> +<p><p>here is a paragraph.<p>here is another paragraph.</p> +</div> + +<h2><a name="h-4.4" id="h-4.4">4.4.</a> Attribute values must always be quoted</h2> + +<p>All attribute values must be quoted, even those which appear to be numeric.</p> + +<p><strong><em>CORRECT: quoted attribute values</em></strong></p> + +<div class="good"> +<p><td rowspan="3"></p> +</div> + +<p><strong><em>INCORRECT: unquoted attribute values</em></strong></p> + +<div class="bad"> +<p><td rowspan=3></p> +</div> + +<h2><a name="h-4.5" id="h-4.5">4.5.</a> Attribute Minimization</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> + +<p><strong><em>CORRECT: unminimized attributes</em></strong></p> + +<div class="good"> +<p><dl compact="compact"></p> +</div> + +<p><strong><em>INCORRECT: minimized attributes</em></strong></p> + +<div class="bad"> +<p><dl compact></p> +</div> + +<h2><a name="h-4.6" id="h-4.6">4.6.</a> Empty Elements</h2> + +<p>Empty elements must either have an end tag or the start tag must end with <code>/></code>. For instance, <code><br/></code> or <code><hr></hr></code>. See <a href= +"guidelines.html#guidelines">HTML Compatibility Guidelines</a> for information on ways to ensure this is backward compatible with HTML 4 user agents.</p> + +<p><strong><em>CORRECT: terminated empty elements</em></strong></p> + +<div class="good"> +<p><br/><hr/></p> +</div> + +<p><strong><em>INCORRECT: unterminated empty elements</em></strong></p> + +<div class="bad"> +<p><br><hr></p> +</div> + +<h2><a name="h-4.7" id="h-4.7">4.7.</a> White Space handling in attribute values</h2> + +<p>When user agents process attributes, they do so according to <a href="http://www.w3.org/TR/REC-xml#AVNormalize">Section 3.3.3</a> of [<a class="nref" href="references.html#ref-xml">XML</a>]:</p> + +<ul> +<li>Strip leading and trailing white space.</li> + +<li>Map sequences of one or more white space characters (including line breaks) to a single inter-word space.</li> +</ul> + +<h2><a name="h-4.8" id="h-4.8">4.8.</a> Script and Style elements</h2> + +<p>In XHTML, the script and style elements are declared as having <code>#PCDATA</code> content. As a result, <code><</code> and <code>&</code> will be treated as the start of markup, and +entities such as <code>&lt;</code> and <code>&amp;</code> will be recognized as entity references by the XML processor to <code><</code> and <code>&</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> +<script type="text/javascript"> +<![CDATA[ +... unescaped script content ... +]]> +</script> +</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 class="nref" href="references.html#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.</a> SGML exclusions</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 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.html#prohibitions">Element Prohibitions</a>.</p> + +<h2><a name="h-4.10" id="h-4.10">4.10.</a> The elements with 'id' and 'name' attributes</h2> + +<p>HTML 4 defined the <code>name</code> attribute for the elements <code>a</code>, <code>applet</code>, <code>form</code>, <code>frame</code>, <code>iframe</code>, <code>img</code>, and <code> +map</code>. HTML 4 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 on the elements listed above. See the <a href="guidelines.html#guidelines">HTML Compatibility Guidelines</a> for information on ensuring such anchors are backward 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> + +<h2><a name="h-4.11" id="h-4.11">4.11.</a> Attributes with pre-defined value sets</h2> + +<p>HTML 4 and XHTML both have some attributes that have pre-defined and limited sets of values (e.g. the <code>type</code> attribute of the <code>input</code> element). In SGML and XML, these are +called <em>enumerated attributes</em>. Under HTML 4, the interpretation of these values was <em>case-insensitive</em>, so a value of <code>TEXT</code> was equivalent to a value of <code>text</code>. +Under XML, the interpretation of these values is <em>case-sensitive</em>, and in XHTML 1 all of these values are defined in lower-case.</p> + +<h2><a name="h-4.12" id="h-4.12">4.12.</a> Entity references as hex values</h2> + +<p>SGML and XML both permit references to characters by using hexadecimal values. In SGML these references could be made using either &#Xnn; or &#xnn;. In XML documents, you must use the +lower-case version (i.e. &#xnn;)</p> + +<hr /> +<div class="navbar">[<a href="normative.html">previous</a>]   [<a href="issues.html">next</a>]   [<a href="Cover.html#toc">table of contents</a>]</div> +</body> +</html> + |