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Attribute “xmlns:og” not allowed here.

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

As an example, the following is the Open Graph protocol markup for The Rock on IMDB:

<!DOCTYPE html>
<html lang="en" prefix="og:">
<title>The Rock (1996)</title>
<meta property="og:title" content="The Rock" />
<meta property="og:type" content="" />
<meta property="og:url" content="" />
<meta property="og:image" content="" />

Learn more:

* W3C: @xmlns deprecation

* Open Graph Protocol

Related W3C validator issues

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