The main objective of HTML5 is not degrading any of the existing content on the internet. There is over 20 years of HTML data on the internet and HTML5 will be able to handle all that legacy data without problems.
The main objective of HTML5 utility is to keep users in control. As a result, HTML5 design is geared towards user experience and not HTML5 author’s wishes and desires.
HTML5 is also resulted in the creation of XTHML5 that enables XML integration and valid HTML5 code generation.
HTML5 has security built into each part of specification. As a result, HTML5 security considerations were built into HTML5 from the start. HTML5 follows new origin-based security model which is easier to use and it is more consistent with the different APIs.
Separation of layers
HTML5 goes extra mile into separating content from the markup tags. It uses CSS heavily in achieving this objective. Old markups will not be supported but will be rendered by HTML5.
HTML5 supports new DOCTYPE, new set of declarations and simple APIs
HTML5 is designed to handle errors more gracefully than prior versions of HTML. It provides error handling plans that can be used to recover from errors. Moreover, errors will not result in broken pages but rather in malformed HTML page rendering so that user can see content.
HTML5 is designed to be more accessible than ever. It works well with Web Accessibility Initiative (WAI) and Accessible Rich Internet Applications (ARIA). It will work across all different devices and platforms. HTML5 has superior support for worldwide languages and tags can be defined in multiple languages other than English.