sibling vs neighbor

I see some people use neighbor in the cache_host directive.
I can't find any reference to neighbor, if it's different to sibling or
parent, could someone please explain the difference.
And if it's documented somewhere, please let me know where.

Thanks.

Mervyn Jack, Technical Services, Country Netlink, Cobram, Vic, Australia.
Providing Internet access to the Cobram, Shepparton & Benalla local call
areas.
Phone 03 5871 1000 | Fax 03 5871 1874 | Mobile 019 438419
Work: http://www.cnl.com.au | Personal: http://www.cnl.com.au/~mervynj
Received on Wed Jul 30 1997 - 03:31:07 MDT