<h2><a name=separation>Separation of Structure and Presentation</a></h2>
<p>By <a href="deprecated.html">deprecating</a> many presentational features from <a href="http://www.htmlhelp.com/reference/wilbur/">HTMLá3.2</a> and adding hooks for style sheets, HTMLá4.0 encourages separating a document's structure from its presentation. This concept is key to understanding HTMLá4.0.</p>
<p>When authors use <abbr class=initialism title="HyperText Markup Language">HTML</abbr> to markup a document's structure and <a href="http://www.htmlhelp.com/reference/css/">style sheets</a> to suggest the document's presentation, they can more easily achieve the device-independence that helped bring <abbr class=initialism title="HyperText Markup Language">HTML</abbr> its initial popularity. A document with a rich structure can be presented in many different ways on different media, allowing the document to adjust to new technologies such as phone or in-car aural browsers. The separation of content and presentation also allows authors to change the presentation of an entire site by editing a single style sheet, providing significant advantages in site maintenance.</p>
<h2><a name=accessibility>Accessibility</a></h2>
<p>Many of HTML 4.0's improvements in the area of accessibility follow from its emphasis on the separation of structure and presentation. When <abbr class=initialism title="HyperText Markup Language">HTML</abbr> is used structurally, a document can adapt to different browsing environments, accommodating large fonts, special colors, speech synthesizers, and Braille tactile feedback devices. This adaptability allows blind, low-vision, colorblind, and cognitively-challenged users access to the Web, opening a door for the world's 600 million disabled people.</p>
<p>HTML 4.0 includes many new elements and attributes aimed at improving the Web's accessibility. The multi-dimensional nature of <abbr class=initialism title="HyperText Markup Language">HTML</abbr> tables has long posed problems for non-visual browsing, but new attributes on the <strong class=html><a href="tables/table.html">TABLE</a></strong>, <strong class=html><a href="tables/th.html">TH</a></strong>, and <strong class=html><a href="tables/td.html">TD</a></strong> elements allow table summaries and a more explicit association between a cell and its header information. These attributes give non-visual browsers the ability to render a cell's header information, possibly in an abbreviated form, before giving the cell's content.</p>
<p>New elements in HTML 4.0 also bring accessibility improvements to forms. The new <strong class=html><a href="forms/fieldset.html">FIELDSET</a></strong> element allows form controls to be grouped together and the <strong class=html><a href="forms/legend.html">LEGEND</a></strong> element provides a caption for the group. By grouping related form controls, authors allow those with non-visual browsers to more easily navigate complicated forms. As well, the new <strong class=html><a href="forms/label.html">LABEL</a></strong> element associates a text label with a form control so that users can more easily determine what information is required in a given field.</p>
<p>Other accessibility improvements include full image descriptions through the <strong class=html>LONGDESC</strong> attribute on the <strong class=html><a href="special/img.html">IMG</a></strong> element, rich alternatives to images and videos through the <strong class=html><a href="special/object.html">OBJECT</a></strong> element, and richer alternatives to image maps through a new content model for the <strong class=html><a href="special/map.html">MAP</a></strong> element.</p>
<h2><a name=i18n>Internationalization</a></h2>
<p>To allow representation of the world's languages, HTMLá4.0 adopts the <em>Universal Character Set</em> as its character set. Previous versions of <abbr class=initialism title="HyperText Markup Language">HTML</abbr> were restricted to ISO-8859-1, a character set that only handled some western European languages. The Universal Character Set is character-by-character equivalent to <a href="http://www.unicode.org/">Unicode</a> 2.0 and contains characters for almost all of the world's languages.</p>
<p>The <strong class=html><a href="attrs.html#lang">LANG</a></strong> and <strong class=html><a href="attrs.html#dir">DIR</a></strong> attributes are new in HTMLá4.0 and apply to almost all elements. These attributes allow authors to specify the language and directionality of text. The <strong class=html><a href="special/bdo.html">BDO</a></strong> element allows authors to override the bidirectional algorithm used when right-to-left text such as Hebrew is presented.</p>
<p>HTML 4.0 also offers new <a href="entities/index.html">entities</a> for easy entry of <a href="entities/symbols.html">mathematical symbols and Greek letters</a> as well as <a href="entities/special.html">other special characters</a>.</p>
<h2><a name=stylesheets>Style Sheets</a></h2>
<p>HTML 4.0 adds new hooks for <a href="http://www.htmlhelp.com/reference/css/">style sheets</a>, which suggest how a document is presented. The new <strong class=html><a href="attrs.html#id">ID</a></strong>, <strong class=html><a href="attrs.html#class">CLASS</a></strong>, and <strong class=html><a href="attrs.html#style">STYLE</a></strong> attributes allow style information to be attached to specific elements. The <strong class=html><a href="head/link.html">LINK</a></strong> and <strong class=html><a href="head/style.html">STYLE</a></strong> elements have new <strong class=html>TYPE</strong> and <strong class=html>MEDIA</strong> attributes for specifying the style sheet language and target media, respectively.</p>
<p>HTML 4.0 embraces client-side scripting through the addition of a number of new attributes. The <strong class=html><a href="special/script.html">SCRIPT</a></strong> element now includes attributes for specifying the scripting language, embedding an external script, and deferring execution of a script. As well, a number of event attributes have been added to enable execution of a script upon events such as the user clicking an element, pressing a key, moving the mouse over an element, or changing the value of a form control.</p>
<p>The <strong class=html><a href="block/noscript.html">NOSCRIPT</a></strong> element, also new in HTMLá4.0, provides alternate content for browsers with client-side scripting disabled or not supported.</p>
<h2><a name=frames>Frames</a></h2>
<p>The inclusion of <a href="frames/index.html">frames</a> in HTMLá4.0 gives authors the ability to present multiple documents in one window. The frames model used in HTMLá4.0 is not changed from the <a href="http://www.htmlhelp.com/design/frames/whatswrong.html" title="What's wrong with frames?">flawed frames model</a> originally proposed by <a href="http://www.netscape.com/">Netscape</a>.</p>
<h2><a name=tables>Advanced Tables</a></h2>
<p>The simple table model of <a href="http://www.htmlhelp.com/reference/wilbur/">HTMLá3.2</a> is expanded in HTMLá4.0 to include row and column groups, greater flexibility in defining a table's rules, and accessibility improvements. The use of row groups (<strong class=html><a href="tables/thead.html">THEAD</a></strong>, <strong class=html><a href="tables/tfoot.html">TFOOT</a></strong>, <strong class=html><a href="tables/tbody.html">TBODY</a></strong>) allows visual browsers to render static header and footer rows with scrollable body rows, thus improving the readability of large tables.</p>
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