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HTML Checking for Large Sites

Rocket Validator integrates the W3C Validator HTML checker into an automated web crawler.

All HTML documents must start with a <!DOCTYPE> (Document Type Declaration), that informs browsers about the type and version of HTML used to build the document. In HTML5, this is simply <!DOCTYPE html> and must appear at the start of the document.

Here is an example of a minimal HTML document, including the Document Type Declaration at its start:

<!DOCTYPE html>

Related W3C validator issues