Some questions about CrawlRequest

hello,  I've relly been checking the code of AN, but there are some trouble for me. I hope get your help, thanks!

     1、what do these enum items mean?    public enum UriClassificationType : byte
    {
        None = 0,
        Domain = 1,
        Extension = 2,
        FileExtension = 4,
        Host = 8,
        Scheme = 16
    }
    2、In the DiscoveryManager.cs, what is the meaning and difference between the function IsCrawlRestricted and IsDiscoveryRestricted()?     /// <summary>
        /// Determines whether the specified crawl request is restricted.
        /// </summary>
        /// <param name="crawlRequest">The crawl request.</param>
        /// <param name="absoluteUri">The absolute URI.</param>
        /// <returns>
        ///  <c>true</c> if the specified crawl request is restricted; otherwise, <c>false</c>.
        /// </returns>
        internal static bool IsCrawlRestricted(CrawlRequest crawlRequest, string absoluteUri)
        {
        }         /// <summary>
        /// Determines whether [is discovery restricted] [the specified crawl request].
        /// </summary>
        /// <param name="crawlRequest">The crawl request.</param>
        /// <param name="absoluteUri">The absolute URI.</param>
        /// <returns>
        ///  <c>true</c> if [is discovery restricted] [the specified crawl request]; otherwise, <c>false</c>.
        /// </returns>
        internal static bool IsDiscoveryRestricted(CrawlRequest crawlRequest, string absoluteUri)
        {
        }
       3、if I actually want to get the specific data I really want to, i just write code in here
   if (extractWebPageMetaData)
                {
                }           And have a limit on the priority when Adding CrawlRequest to be crawled in the CrawlRequestManager.cs(ProcessHyperLinks).
         if (!DiscoveryManager.IsCrawlRestricted(crawlRequest, hyperLinkDiscovery.Uri.AbsoluteUri))
                            {
                            }
          Do I have any other methods to do that? If not ,i think AN could provide user with a interface class which user can modify to crawl the special content with a good efficiency.  it is very useful for user.
          Thank you!
          baby_zrq