Microsoft Visual Studio 2010 Service Pack 1
Although initially released without HTML5 support, Microsoft Visual Studio 2010 added some capabilities with SP1, released in March 2011 and updated three months later. With IntelliSense, elements specific to HTML5 have been added; IntelliSense is intended to make language references easily accessible by recognizing commands. HTML5 validation is supported as well, to make sure code works and conforms to standards.
After installing the service pack, developers must tell Visual Studio to start using the HTML5 schema. SP1 makes it easier to build HTML5 and CSS3 Web applications on top of ASP.Net, according to Microsoft.