HTML5 has been developed considering current and future browser development and past, present, and future web development work. Due to this, HTML5 gained significant momentum. Driven by practicality, it has emerged as the W3C’s choice for accelerated development.

HTML5 is backward compatible and it contains all the features of the HTML4 spec, though with a few changes and improvements. It also contains additional capabilities for BUILDING dynamic web APPLICATIONS and creating higher quality markup.

Features of HTML5

• New Semantic elements to allow us to define more parts of our markup unambiguously and semantically rather than using lots of classes and IDs.
• APIs for adding video, audio, scriptable graphics, and other rich application type content to our sites.
• HTML5 has been deliberately built to compete with proprietary plug-ins such as FLASH and Silverlight.
• New features for standardizing functionality that we already built in bespoke, hacky ways. Server-sent updates and form validation spring to mind immediately.
• Microdata: Microdata allows machine-readable data to be embedded in HTML documents so that browsers and search engines can extract data from the page.  
• Web Workers: Allows a JavaScript operation to work in the background without interfering with the user’s browsing.
• Web Storage: This is a more powerful form of a cookie. It can store a large amount of data on the client side. It can store up to 5MB of data, whereas a cookie is limited to about 4KB.
• Web Sockets: Allows pages to use the WebSocket protocol to send two-way messages between a browser and a server.
• Cross-document and channel messaging: Cross-document messaging provides a capability to exchange documents regardless of the source domain and without enabling cross-site attacks. Channel messaging uses independent pieces of code blocks to communicate directly.
• Server sent events: Using this feature, push notifications can be sent from a server to a client browser as DOM events.
• New features to plug gaps in the functionality we traditionally had available in OPEN standards, such as defining how browsers should handle markup errors, allowing web apps to work offline, allowing us to use always-open socket connections for app data TRANSFER, and again, audio, video and scriptable images (canvas).