As most of you have already heard about HTML5 and CSS3 , which are the next generation web technologies and so most of the web sites are migrating to them.
These are already supported by latest versions of many browsers including mobile browsers.
Beyond Microsoft’s involvement with the W3C and the HTML5 technologies supported in the browser, there’s another dimension to Microsoft’s approach to HTML5 that’s important for developers: its approach to HTML5 tooling. In early 2011, Microsoft updated two of its development tools with service packs: Visual Studio 2010 and Expression Web 4. The service packs for both of these tools provided an HTML5 document type for validation, as well as IntelliSense for new HTML5 tags and attributes
WebMatrix makes it easier for you by providing an HTML5 document by default.