HTML5 introducection

HTML5 introduces
a number of new elements and attributes that reflect typical usage on modern websites. Some of them are semantic replacements for common uses of generic block (<div>) and inline (<span>) elements, for example <nav> (website navigation block), <footer> (usually referring to bottom of web page or to last lines of HTML code), or <audio> and <video> instead of <object>.Some deprecated elements from HTML 4.01 have been dropped, including purely presentational elements such as <font> and <center>, whose effects have long been superseded by the much more powerful Cascading Style Sheets.

When you use the new HTML5 DOCTYPE, it triggers browsers to render the page in standardscompliant
mode. As you may know, Web pages can have different rendering modes, such as Quirks,
Almost Standards, and Standards (or no-quirks) mode. The DOCTYPE indicates to the browser which
mode to use and what rules are used to validate your pages.