HTML5, which aims to make HTML more useful for creating web applications as well as semantically marked up documents, is not yet a formal Recommendation as of this writing, however, it is beginning to gain browser support and is already being used for web and mobile application development.
HTML5 uses HTML 4.01 and the legacy behavior of browsers as a starting point, using the Document Object Model (DOM, the “tree” formed by a document’s structure) as its basis rather than a particular set of syntax rules. HTML5 can be written with HTML syntax (called the HTML serialization of HTML5) or according to the stricter syntax of XML (XML serialization, or “XHMTL 5”) if XML parsing is required.
Because HTML5 is still in development, the details are changing rapidly. The HTML5 elements and attributes in this book are based on the WHATWG HTML5 Working Draft dated December 9, 2009.
For the most recent version, go to www.whatwg.org/specs/web-apps/current-work/multipage/. For a list of the ways HTML5 differs from HTML 4.01, see dev.w3.org/html5/html4-differences.
HTML5 offers new features (elements, attributes, event handlers, and APIs) for easier web application development and more sophisticated form handling. There are also new semantic elements for marking up page content. Most of the purely presentational or poorly supported elements and attributes in HTML 4.01 have been dropped from HTML5, however, a few have been redefined or reinstated.
Details for each ...