Many popular browsers have already started supporting HTML5 features in their latest versions. However, none of them support 100% of the recommendations yet, but are expected to do so in near future.
HTML5 is more powerful and gives more flexibility to developers. The key differences between HTML5 and previous HTML versions are:
There are different types of doctype declarations in previous versions, but HTML5 has only one:
If the page starts with this doctype declaration, then the browsers understand that it is written in HTML5.
Websites have two types of audiences - humans and programmes such as crawlers. (Eg: Googlebot, Bingbot etc are bots or spiders used by search engines to find and index webpages). HTML5 semantics makes the website more readable to bots. HTML5 has new elements and also added more meaning to existing elements.
New semantic elements with more meaningful roles in HTML5 are:
<header>, <nav>, <article>, <section>, <footer>
These tags work just like the <div> tag, but from SEO perspective they give different weight to the contents. This means that bots can read them just the way humans do.
New meanings added to existing elements such as <strong> and <em>. Visually they do the same job as <b> but <strong> has a new meaning that tells the crawlers that the text enclosed is more important, and <em> tells them that the text has to be emphasised.
For humans the text wrapped in <strong> and <em> look the same like those wrapped in <b> and <i>. But <b> and <i> dont carry any extra meaning from SEO perspective whereas <strong> and <em> do, that is the text is important.
Previous versions of HTML5 needed third party tools like flash to play audio and video. HTML5 has new media elements <video> and <audio> and inbuilt features which means it can handle media content by itself.
Making web applications is easier and new APIs are available for this. Examples are APIs for playing video and audio, API for exposing history, API for offline applications etc.
Error handling has been standardized so that malformed content is displayed by different browsers in the same way. This is greatly helpful for new browser developers and also reduce the testing and validation required before launching a new browser.
Some elements like <font> , <centre>, <strike> have been removed because this can be achieved by CSS.
It is expected that HTML5 would soon be the standard of the web. It would be a good idea to make use of the enhanced features of HTML5 (the ones already being supported by the leading web browsers) in your web development.