private static final String META_NAME_THUMBNAIL_CONTENT = "//META[@name=\"thumbnail\" or @name=\"THUMBNAIL\"]/@content";

    private static final String META_PROPERTY_OGIMAGE_CONTENT = "//META[@property=\"og:image\"]/@content";

    private static final String META_NAME_ROBOTS_CONTENT = "//META[@name=\"robots\" or @name=\"ROBOTS\"]/@content";

    private static final String ROBOTS_TAG_NONE = "none";