HTML Checking for Large Sites
Rocket Validator integrates the W3C Validator HTML checker into an automated web crawler.
Attribute with the local name “xmlns:(fb|og)” is not serializable as XML 1.0
xmlns:og attributes have been deprecated. If you’re using Facebook / Open Graph Protocol proprietary tags in you document, you can update the markup to the new syntax.
Related W3C validator issues
FBML - Facebook Markup Language was used to embed Facebook-specific tags on web sites, was retired in 2011 but this still appears on <html> tags on some sites. You should consider removing this from your site and use alternative ways to do that.
The old way for using Open Graph Protocol tags in web pages is not valid HTML5, you should use the updated markup as specified in https://ogp.me
As an example, the following is the Open Graph protocol markup for The Rock on IMDB:
<!DOCTYPE html> <html lang="en" prefix="og: https://ogp.me/ns#"> <head> <title>The Rock (1996)</title> <meta property="og:title" content="The Rock" /> <meta property="og:type" content="video.movie" /> <meta property="og:url" content="https://www.imdb.com/title/tt0117500/" /> <meta property="og:image" content="https://ia.media-imdb.com/images/rock.jpg" /> </head> </html>
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