* tag. This takes care of that. */ add_filter( 'language_attributes', 'cd_fbspw_ie_fix', 99 ); function cd_fbspw_ie_fix( $atts ) { // if the string already has what we need, bail if( preg_match( '/xmlns:fb="(.*)"/', $atts ) ) return $atts; $atts .= ' xmlns:fb="http://ogp.me/ns/fb#"'; return $atts; }