Visual Studio 2010 was originally released without HTML5 support, so does SP1 finally add support for it, revealed a member of the Microsoft Visual Web Developer team. The entire HTML5 specification isn't supported but most of the new elements and attributes are. That means you get both intellisense and validation for HTML5 with SP1.
"After installing SP1 you've to tell VS to start using HTML5 schema. Go to Tools -> Options, and then select Text Editor -> HTML -> Validation. You should now be able to select HTML5 or XHTML5 as the target schema.
Or if you've the HTML Source Editing toolbar enabled, you can select it in the target schema dropdown.
Also, in SP1 are a few improvements in the CSS3 support as well, though not as elaborate as with HTML5. The editor now supports the more advanced selectors such as div:nth-child(2n+1) without giving validation errors and the new color values rgba, hsl, hsla and 8 digit hex values are also supported.
"We encourage all ASP.NET developers to start taking advantage of what HTML5 and CSS3 has to offer already today. The Web Platform and Tools team takes web standards very seriously and you will see much better support for HTML5 and CSS3 in the future," Microsoft added.