我找到了这个解决方案meta 到valid_children （未测试）：

// Prevent TinyMCE from stripping out schema.org metadata
// https://snipt.net/jamesw/prevent-tinymce-from-stripping-schemaorg-attributes-in-wordpress/
function schema_TinyMCE_init( $in ) {
    /**
     *   Edit extended_valid_elements as needed. For syntax, see
     *   http://www.tinymce.com/wiki.php/Configuration:valid_elements
     *
     *   NOTE: Adding an element to extended_valid_elements will cause TinyMCE to ignore
     *   default attributes for that element.
     *   Eg. a[title] would remove href unless included in new rule: a[title|href]
     */
    if ( ! empty( $in[\'extended_valid_elements\'] ) ) {
            $in[\'extended_valid_elements\'] .= \',\';
    }
    $in[\'extended_valid_elements\'] .= \'@[id|class|style|title|itemscope|itemtype|itemprop|datetime|rel],div,dl,ul,dt,dd,li,span,meta[!content],a|rev|charset|href|lang|tabindex|accesskey|type|name|href|target|title|class|onfocus|onblur]\',

    if ( !empty( $in[\'valid_children\'] ) ) {
        $in[\'valid_children\'] .= \',\';
    }
    $in[\'valid_children\'] .= \'+body[meta],+div[meta]\';

    return $in;
}
add_filter(\'tiny_mce_before_init\', \'schema_TinyMCE_init\' );