You’ve already learned a lot about HTML5. Whether you’ve written a new HTML5 document from scratch or made incremental updates to your existing HTML4 or XHTML1 documents, it’s time to make sure that your changes are correct.

The W3C Validator at http://validator.w3.org has long been an indispensable tool for modern web designers and developers alike. The W3C Validator has been updated to validate HTML5 documents automatically by detecting the HTML5 <!DOCTYPE html>. When you run the W3C Validator on your site, if everything is correct, you’ll see something like the following results page.

The “Result: Passed, ...

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