A Preview of HTML 5
Abstract
The web is constantly evolving. New and innovative websites are being created
every day, pushing the boundaries of HTML in every direction. HTML 4 has
been around for nearly a decade now, and publishers seeking new techniques to
provide enhanced functionality are being held back by the constraints of
the language and browsers.
To give authors more flexibility and interoperability, and enable more interactive
and exciting websites and applications, HTML 5 introduces and enhances a wide range of features including form controls, APIs, multimedia, structure, and semantics.
Work on HTML 5, which commenced in 2004, is currently being carried out in
a joint effort between the
W3C HTML
WG and
the WHATWG.
Many key players are participating in the W3C effort including representatives
from the four major browser vendors: Apple, Mozilla, Opera, and Microsoft;
and a range of other organisations and individuals with many diverse interests
and expertise.
Note that the
specification is still a work in progress and quite a long
way from completion. As such, it is possible that any feature discussed in
this article may change in the future. This article is intended to provide
a brief introduction to some of the major features as they are in the current
draft.
Structure
HTML 5 introduces a whole set of new elements that make it much easier to
structure pages. Most HTML 4 pages include a variety of common structures,
such as headers, footers and columns and today, it is fairly common to mark
them up using div elements, giving each a descriptive id or class.
Diagram illustrates a typical two-column layout marked up using divs with id and class attributes. It contains a header, footer, and horizontal navigation bar below the header. The main content contains an article and sidebar on the right.
The use of div elements is largely because current versions of
HTML 4 lack the necessary semantics for describing these parts more specifically.
HTML 5 addresses this issue by introducing new elements for representing
each of these different sections.
The div elements can be replaced with the new elements: header, nav, section, article, aside, and footer.
The markup for that document could look like the following:
<body>
<header>...</header>
<nav>...</nav>
<article>
<section>
...
</section>
</article>
<aside>...</aside>
<footer>...</footer>
</body>
There are several advantages to using these elements. When used in conjunction
with the heading elements (h1 to h6), all of these provide
a way to mark up nested sections with heading levels, beyond the six levels
possible with previous versions of HTML. The specification includes a
detailed algorithm for generating an outline that takes the structure of these elements
into account and remains backwards compatible with previous versions. This
can be used by both authoring tools and browsers to generate tables of contents
to assist users with navigating the document.
For example, the following markup structure marked up with nested section and h1 elements:
<section>
<h1>Level 1</h1>
<section>
<h1>Level 2</h1>
<section>
<h1>Level 3</h1>
</section>
</section>
</section>
Note that for better compatibility with current browsers, it is also possible
to make use of the other heading elements (h2 to h6) appropriately in place
of the h1 elements.
By identifying the purpose of sections in the page using specific sectioning
elements, assistive technology can help the user to more easily navigate
the page. For example, they can easily skip over the navigation section or
quickly jump from one article to the next without the need for authors to provide
skip links. Authors also benefit because replacing many of the divs in the
document with one of several distinct elements can help make the source code
clearer and easier to author.
The header element represents the header of a section. Headers may contain
more than just the section’s heading—for example it would be reasonable
for the header to include sub headings, version history information or bylines.
<header> <h1>A Preview of HTML 5</h1> <p class="byline">By Lachlan Hunt</p> </header>
<header> <h1>Example Blog</h1> <h2>Insert tag line here.</h2> </header>
The footer element represents the footer for the section it applies to. A
footer typically contains information about its section such as who wrote it,
links to related documents, copyright data, and the like.
<footer>© 2007 Example Inc.</footer>
The nav element represents a section of navigation links. It is suitable
for either site navigation or a table of contents.
<nav>
<ul>
<li><a href="/">Home</a></li>
<li><a href="/products">Products</a></li>
<li><a href="/services">Services</a></li>
<li><a href="/about">About</a></li>
</ul>
</nav>
The aside element is for content that is tangentially related to the content
around it, and is typically useful for marking up sidebars.
<aside>
<h1>Archives</h1>
<ul>
<li><a href="/2007/09/">September 2007</a></li>
<li><a href="/2007/08/">August 2007</a></li>
<li><a href="/2007/07/">July 2007</a></li>
</ul>
</aside>
The section element represents a generic section of a document or application,
such as a chapter, for example.
<section>
<h1>Chapter 1: The Period</h1>
<p>It was the best of times, it was the worst of times,
it was the age of wisdom, it was the age of foolishness,
it was the epoch of belief, it was the epoch of incredulity,
it was the season of Light, it was the season of Darkness,
...</p>
</section>
(Excerpt from A Tale of Two Cities)
The article element represents an independent section of a document, page
or site. It is suitable for content like news or blog articles, forum posts
or individual comments.
<article id="comment-2">
<header>
<h4><a href="#comment-2" rel="bookmark">Comment #2</a>
by <a href="http://example.com/">Jack O'Niell</a></h4>
<p><time datetime="2007-08-29T13:58Z">August 29th, 2007 at 13:58</time>
</header>
<p>That's another great article!</p>
</article>
Video and Audio
In recent years, video and audio on the web has become increasingly viable
and sites like YouTube, Viddler, Revver, MySpace, and dozens of others are
making it easy for anyone to publish video and audio. However, since HTML currently
lacks the necessary means to successfully embed and control multimedia itself,
many sites are relying on Flash to provide that functionality. Although it
is possible to embed multimedia using various plug-ins (such as QuickTime,
Windows Media, etc.), Flash is currently the only widely deployed plugin
that provides a cross-browser compatible solution with the desired APIs for
developers.
As evidenced by the various Flash-based media players, authors are interested
in providing their own custom-designed user interfaces, which generally allow
users to play, pause, stop, seek, and adjust volume. The plan is to provide
this functionality in browsers by adding native support for embedding video
and audio and providing DOM APIs for scripts to control the playback.
The new video and audio elements make this really easy. Most of the APIs
are shared between the two elements, with the only differences being related
to the inherent differences between visual and non-visual media.
Both Opera and WebKit have
released builds with partial support for the video element. You may download
the experimental
build of Opera or a recent nightly
build of WebKit to try out these examples. Opera includes support for Ogg
Theora and WebKit supports all the formats that are supported by QuickTime,
including third party codecs.
The simplest way to embed a video is to use a video element and allow
the browser to provide a default user interface. The controls attribute is
a boolean attribute that indicates whether or not the author wants this UI
on or off by default.
<video src="video.ogv" controls poster="poster.jpg"
width="320" height="240">
<a href="video.ogv">Download movie</a>
</video>
The optional poster attribute can be used to specify an image which will be
displayed in place of the video before the video has begun playing. Although
there are some video formats that support their own poster frame feature, such
as MPEG-4, this provides an alternative solution that can work independently
of the video format.
It is just as simple to embed audio into a page using the audio element. Most
of the attributes are common between the video and audio elements, although
for obvious reasons, the audio element lacks the width, height, and poster attributes.
<audio src="music.oga" controls>
<a href="music.oga">Download song</a>
</audio>
HTML 5 provides the source element for specifying alternative
video and audio files which the browser may choose from based on its media type
or codec support. The media attribute can be used to specify a
media query for selection based on the device limitations and the type attribute
for specifying the media type and codecs. Note that when using the source elements,
the src attribute needs
to be omitted from their parent video or audio element
or the alternatives given by the source elements will be ignored.
<video poster="poster.jpg">
<source src="video.3gp" type="video/3gpp"
media="handheld">
<source src="video.ogv" type="video/ogg;
codecs=theora, vorbis">
<source src="video.mp4" type="video/mp4">
</video>
<audio>
<source src="music.oga" type="audio/ogg">
<source src="music.mp3" type="audio/mpeg">
</audio>
For authors who want a little more control over the user interface so that
they can make it fit the overall design of the web page, the extensive API
provides several methods and events to let scripts control the playback of the
media. The simplest methods to use are the play(), pause(), and setting currentTime to rewind to the beginning. The following example illustrates the use of these.
<video src="video.ogg" id="video"></video>
<script>
var video = document.getElementById("video");
</script>
<p><button type="button" onclick="video.play();">Play</button>
<button type="button" onclick="video.pause();">Pause</button>
<button type="button" onclick="video.currentTime = 0;">
<< Rewind</button>
There are many other attributes and APIs available for the video and audio
elements that have not been discussed here. For more information, you should
consult the current
draft specification.
Document Representation
Unlike previous versions of HTML and XHTML, which are defined in terms of
their syntax, HTML 5 is being defined in terms of the Document Object Model
(DOM)—the tree representation used internally by browsers to represent the
document. For example, consider a very simple document consisting of a title,
heading and paragraph. The DOM tree could look something like this:
The DOM tree includes a title element in the head and h1 and p elements in the body.
The advantage of defining HTML 5 in terms of the DOM is that the language
itself can be defined independently of the syntax. There are primarily two
syntaxes that can be used to represent HTML documents: the HTML serialisation
(known as HTML 5) and the XML serialisation (known as XHTML 5).
The HTML serialisation refers to the syntax that is inspired by the SGML
syntax from earlier versions of HTML, but defined to be more compatible with
the way browsers actually handle HTML in practice.
<!DOCTYPE html>
<html>
<head>
<title>An HTML Document</title>
</head>
<body>
<h1>Example</h1>
<p>This is an example HTML document.
</body>
</html>
Note that like previous versions of HTML, some tags are optional and are automatically
implied.
The XML serialisation refers to the syntax using XML 1.0 and namespaces,
just like XHTML 1.0.
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>An HTML Document</title>
</head>
<body>
<h1>Example</h1>
<p>This is an example HTML document.</p>
</body>
</html>
Excluding differences in whitespace and the presence of the xmlns attribute,
those two examples are equivalent.
Browsers use the MIME type to distinguish between the two. Any document served
as text/html must conform to the requirements for the HTML serialisation
and any document served with an XML MIME type such as application/xhtml+xml must conform to the requirements for the XML serialisation.
Authors should make an informed choice about which serialisation to use,
which may be dependent on a number of different factors. Authors should not
be unconditionally forced to use one or the other; each one is optimised
for different situations.
Benefits of Using HTML
- Backwards compatible with existing browsers
- Authors are already familiar with the syntax
- The lenient and forgiving syntax means there will be no user-hostile “Yellow
Screen of Death” if a mistake accidentally slips through - Convenient shorthand syntax, e.g. authors can omit some tags and attribute values
Benefits of Using XHTML
- Strict XML syntax encourages authors to write well-formed markup, which
some authors may find easier to maintain - Integrates directly with other XML vocabularies, such as SVG and MathML
- Allows the use of XML Processing, which some authors use as part of their
editing and/or publishing processes
How to Contribute
Work on HTML 5 is rapidly progressing, yet it is still expected to continue
for several years. Due to the requirement to produce test cases and achieve
interoperable implementations, current estimates have work finishing in around
ten to fifteen years. During this process, feedback from a wide range of
people including, among others, web designers and developers, CMS and authoring
tool vendors, and browser vendors is vital to ensure its success. Everyone
is not only welcome, but actively encouraged to contribute feedback on HTML
5.
In addition to the specification, there are several other related efforts
designed to help people better understand the work.
- The Differences from
HTML 4 describes the changes that have occurred since
the previous version of HTML. - The HTML Design Principles discuss principles used to help make decisions,
and will help you understand the rationale behind many of the current
design decisions. - The Web Developer’s Guide
to HTML 5, which only recently began, is being
written to help web designers and developers understand everything they
need to know to write conforming HTML 5 documents, and provide guidelines
and describe best practices.