HTML5 is cooperation between the World Wide Web Consortium (W3C) and the Web Hypertext Application Technology Working Group (WHATWG).
WHATWG was working with web forms and applications, and W3C was working with XHTML 2.0. In 2006, they decided to cooperate and create a new version of HTML.
Cleaner markup / Improved Code
HTML 5 will enable web designers to use cleaner, neater code, we can remove most div tags and replace them with semantic HTML 5 elements.
Now it is easy to see which parts of the page are headers, navigation menu, footers etc as the tags are specific for these all. By using HTML5 elements we can increase the semantic value of the web page as the codes are very standardized.
As websites adopt the new HTML5 elements we will see greater consistency in terms of the HTML used to code a web page on one site compared to another. This will make it easier for designers and developers to immediately understand how a web page is structured.
Different technologies can elaborate on the features with the help of HTML5, as they can immediately make more detailed understanding of the structure of a page by take a look at HTML5 elements it has.
Fulfill the need of Web application
Many new features and standards have emerged as part of HTML 5. Once you detect the available features in today’s browsers, you can take advantage of those features in your application. Main focus of HTML5 is to make easier application with easy front-ends, drag and drop tools, discussion boards, wikis and other useful elements.
Offline Application cache
All browsers have some kind of caching memory. If you open up your laptop and click the Back button in the browser to see the previous page that was opened. However, as you are not connected to the internet and the browser didn’t cache the page properly, you are unable to view that page. You then click the Forward button thinking that at least that page will load, but it doesn’t. You need to reconnect to the internet to be able to view the pages. But HTML 5, provides a smarter solution. While building the site, the developer can specify the files that the browser should cache. So, even if you refresh the page when you are offline, the page will still load correctly. This sort of caching has several advantages like offline browsing; files load much faster and reduced load on server.
While cookies have been used to track unique user data for years, they have serious disadvantages. The largest flaw is that all of your cookie data is added to every HTTP request header. This can end up having a measurable impact on response time. So a best practice is to reduce cookie size. With HTML5 you can do better by using sessionStorage and local Storage (two different storage in HTML5.) in place of cookies. It is not a permanent database, but enables you to store structured data, temporarily.
With help of Geolocation any one can find out where you are in the world and sharing that information with people. There is different ways to figure out where you are — your IP address, your wireless network connection, which cell tower your phone is talking to, or dedicated GPS hardware that calculates latitude and longitude from information sent by satellites in the sky. But The new HTML5 geolocation APIs make location, whether generated via GPS or other methods, directly available to any HTML5-compatible browser-based application.
Browser Support: The main problem with HTML5′s acceptance is that only modern browsers support it. By modern, I mean almost everything except for Internet Explorer. The new version…IE9 offers excellent support, but as of this writing it’s not quite out of beta. Even if it were, the majority of people will still use older versions of IE for quite some time. There are things you can do to make the language play nice with older browsers, but none of them are perfect.
The Language is a Spec: Another problem is that although parts of the language are very stable, the language itself is considered a work in progress, so technically, any of the elements could change at any time. The language is not expected to be completed for several years, which complicates things further. Thankfully, a lot of the language is considered stable and ready to use. I think it’s such a great move forward, that you should develop a Graceful Degradation approach to writing your HTML. That simply means writing HTML that will work with older browsers, but will offer users with more modern browsers an enhanced experience.
Media Licensing Issues: Another ugly fact about HTML5 is that because of licensing issues, rich media has to be compressed in multiple formats in order to be compatible with most browsers. So you’ll probably use something like mp3 audio for webkit browsers (safari, chrome), and ogg for Mozilla (Firefox) browsers. It involves a bit more work and it is a pain, but hopefully those issues will be resolved soon.