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This page shows trends for web standards compliance across sites submitted to this service.
Percentage of pages that validate against DOCTYPE.
Percentage of pages marked as "Valid HTML" or "Valid XHTML" that don't validate against DOCTYPE.
A Document Type Declaration, or DOCTYPE, is a piece of HTML code that says which version of HTML is being used. For example: <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">