3.2 Create documents that validate to published formal grammars

If you validate your HTML to a published formal grammar and declare that validation at the beginning of a page, the browser knows where to look for semantics if it needs to.

You should:

• Include a document type declaration referring to a published DTD. Use the DOCTYPE statement as the first line of your HTML file for the particular grammar (e.g. the strict HTML 4.0 DTD) that the code adheres to
• Use checkers to validate documents. For example, see HTML Validation Service at http://validator.w3.org/ and the CSS Validation Service at http://jigsaw.w3.org/css-validator/.