It sends the URL of your page or post to the Validator.nu API to verify that you have valid HTML code. The returned errors are stored in an easy to read report with links to full validation results.
Once the pro plugin is enabled you will find a “Content Filters” tab on the plugin settings page. Simply select the issues to be automatically corrected. As your website is rechecked you will find the issues in your error log disappearing, alternatively you can click the recheck link next to the error to verify that the problem has been resolved.