Index of /specs/pingback

      Name                    Last modified      Size  Description
      Parent Directory                             -   
      translations/           2013-03-11 11:03    -   The pingback specification in different languages
      pingback-1.0-notes      2002-09-24 06:57   85   Pingback 1.0 Specification
      pingback-1.0            2013-03-11 11:04   26K  Pingback 1.0 Specification
      pingback-0.9.3          2003-03-10 06:15   25K  Pingback 0.9.3
      pingback-0.9.2          2003-03-10 06:15   24K  Pingback 0.9.2
      pingback-0.9.1          2003-03-10 06:15   24K  Pingback 0.9.1
      pingback-0.9            2003-03-10 06:15   18K  Pingback 0.9
      pingback                2013-03-11 11:04   26K  The latest version of the pingback specification

Why pingback? Why not referrers?

Referrers are very noisy (spiders include bogus referrers, people come to
sites with only subtly different referrers such as a trailing slash or no
trailing slash, etc); referrers don't give you the permalink of the
originating resource; referrers contain many links from news aggregators,
blog rolls, search engines and other pages which do not contain comments
on the post.

Pingbacks are reliable because they are explicitly requested; pingbacks
have a near perfect signal:noise ratio because they are only triggered by
pages that actually link to the post with comments; the pingback mechanism
is easily extended to provide services such as pingback listing (when a
site asks another for the list of pingbacks).