About extensible search filter

[<lastnite@sahara.sarang.net>]

hi
I read rfc2254 about  LDAP v3 search filter.
but I couldn't understand extensible filter BNF definition
and that examples

        (cn:1.2.3.4.5:=Fred Flintstone)
        (sn:dn:2.4.6.8.10:=Barney Rubble)
        (o:dn:=Ace Industry)
        (:dn:2.4.6.8.10:=Dino)          

can anybody explain about this?
thank you ...