Browser plug-ins: Not dead yet
But for all of HTML 5's new features, users shouldn't expect plug-ins to disappear overnight. The Web has a long history of many competing technologies and media formats, and the inertia of that legacy will be difficult to overcome. It may yet be many years before a pure-HTML 5 browser will be able to match the capabilities of today's patchwork clients.
For example, while Vimeo and YouTube are already experimenting with the HTML 5 video tag, deploying HTML 5 multimedia will not be as easy as it sounds. The W3C's decision not to specify media codecs in the HTML 5 standard means developers cannot guarantee that any one media format will be playable on every possible client device. Apple, Google, and Microsoft are pushing for H.264 video, for example, but open source browsers such as Firefox and Konqueror are unable (or ideologically unwilling) to license the appropriate patents to support that format. Unless this boondoggle can be resolved, Web content authors who need to reach the widest possible audience may be forced to continue to rely on Flash.
Not every legacy application will be rewritten for HTML 5, either. For example, even if Google downplays its own Gears technology in favor of a standards-based approach to local application storage, the Gears API and the HTML 5 application cache API are not identical. Google itself admits that "there is not yet a simple, comprehensive way to take your Gears-enabled application and move it (and your entire userbase) over to a standards-based approach." Until there is one, even users of fully HTML-compliant browsers may be forced to install Gears to support some legacy applications.
In the end, browser market share may be the most significant hurdle for developers interested in making the most of HTML 5. Internet Explorer 6, for all its rendering quirks and inept handling of Web standards, is seemingly the browser that cannot die. Older versions of Firefox, IE, Opera, Safari, and others all have large user bases, and none support HTML 5. Until these legacy browsers are replaced with modern updates, Web developers may be stuck maintaining two versions of their sites: a rich version for HTML 5-enabled users, and a version for legacy browsers that falls back on outdated rendering tricks.
In HTML 5's favor, Apple's iPhone and iPad will not support Flash, but are expected to gain support for HTML 5 features as the standard matures. Similarly, Google's Chrome browser leads the pack in HTML 5 support, and devices based on the company's forthcoming Chrome OS are expected to follow suit. Large Web publishers, however, have traditionally been conservative about standards support; even given a large HTML 5 installed base, it may be years before the Fortune 500 is willing to risk the upgrade.
How to try HTML 5 today
Some voices among the Web development community also urge caution. Although Microsoft plans support for HTML 5 in Internet Explorer 9, for example, the software giant questions the wisdom of claiming support at this early stage. "Saying you are standards-based but then saying you are the most HTML 5-compliant browser does not make sense, because the standard is not [complete] yet," Microsoft's Steven Sinofsky remarked in a recent interview.
Indeed, no organization is more guarded in its estimates of HTML 5 adoption than the W3C itself. The HTML 5 working group does not expect the standard to reach Candidate Recommendation status -- the feature-complete phase of the W3C standards process -- before 2011. Even then, the process of ratifying the standard as a W3C Recommendation is expected to continue until somewhere around 2022. If you're doing the math, that's 21 years from XHTML 1.1 to HTML 5.
By any count, HTML 5 is likely to remain cutting-edge technology for the next five to 10 years. Early adopters who would like to see it in action today can do so, however, albeit in a limited way. A number of pilot projects and demonstration sites that showcase the various capabilities of the new standard are available online; the key is choosing the right browser. Support for HTML 5 features in Firefox is spotty. Browsers based on the WebKit rendering engine, including Chrome and Safari, work best. Ironically, that means Internet Explorer is also an option -- but only with the Chrome Frame plug-in installed.
Web developers, likewise, are free to experiment. Whole sites can be built with code that conforms to the current draft of the HTML 5 specification, although results with current browsers will be spotty. One of the best online resources for would-be HTML 5 developers is Mark Pilgrim's excellent Dive into HTML 5, which includes, among other things, a detailed guide to navigating the complex world of the HTML 5 video element and the various codecs supported by current browsers.
So much work remains to be done on the HTML 5 standard, however, that some organizations are liable to dismiss it as yet another overhyped, up-and-coming technology. That would be a mistake. Standards bodies by their very nature move slowly, but work on HTML 5 is being driven by large, motivated vendors, including Adobe, Apple, Google, Microsoft, the Mozilla Foundation, Opera Software, and others. These companies recognize the need for an upgrade to the HTML standard, and their work is helping to realize its potential. The resulting opportunities for Web developers are too compelling to ignore.