If you are beginning to delve into HTML5 in VS.NET say in a MVC3 project using the Razor engine for example, you will want intellisense support for HTML5. This is not difficult to do, but the 'HTML Source Editing' toolbar may not be shown by default in your VS.NET instance. To add it preform the following steps:
1. Open VS.NET but do not open any specific project. This ensures the changes you make will be for all project's opened.
2. Go to 'View -> Toolbars' and select the 'HTML Source Editing' menu item.
3. To test, open a MVC3 or MVC4 project using the Razor engine and navigate to a .cshtml view. The dropdown will now be active and the default selection will be 'XHTML 1.0 Transitional'. Change it to 'HTML5'.
4. Now try typing in the first few letters of a HTML element or attribute, like the 'Canvas' tag.
You now have the HTML5 schema validation and intellisense support.