How to: Select Validation Schemas for HTML Editing in Visual Web Developer
The Visual Studio HTML editor can check the markup in your page and indicate when elements, attributes, or values are not valid. The editor determines what is valid based on the currently selected browser schema. For example, if you have set the browser to Internet Explorer 6, the editor compares the markup in your page against a schema that defines what Internet Explorer 6 considers valid HTML. For more information, see.
To select a validation schema for HTML editing using the HTML Source Editing toolbar
In the HTML Source Editing toolbar, select a schema from the Target Schema for Validation drop-down list. The default is Internet Explorer 6.0.
To select a validation schema for HTML editing using the Options dialog box
On the Tools menu, click Options.
In the Options dialog box, expand the Text Editor node and the HTML node, and then click Validation.
From the Target list, select the schema that you want to use for validation and then click OK.