/** Indicates the start of a crawling process. */
    START_CRAWLING,
    /** Indicates the cleanup phase of crawling. */
    CLEANUP_CRAWLING,
    /** Indicates an unsupported URL was encountered when crawling started. */
    UNSUPPORTED_URL_AT_CRAWLING_STARTED,
    /** Indicates checking the last modified date of a resource. */
    CHECK_LAST_MODIFIED,
    /** Indicates the resource has not been modified. */
    NOT_MODIFIED,