Select the schema to validate against. Each schema determines the elements (tags and attributes) and capitalization that is valid in that schema.
The schema you select also determines what tags and attributes the editor makes available in IntelliSense.
Select the check box to enable validation. If the check box is not selected, the editor will not mark validation errors.
The remaining check boxes allow you to fine-tune validation by specifying individual types of errors that you want the editor to mark.
Some schemas do not offer options to mark individual types of errors. For example, if you select the target XHTML 1.1 Strict, all option check boxes are disabled because all types of errors are marked.