This plug-in is Relationship Completer, a great tool that does exactly what it says: it completes relationships. Once you install Relationship Completer by placing the plug-in file in ~/Library/Address Book Plug-ins and restarting Address Book, the plug-in will add another item to the contextual menu that pops up when you click on the field title to the left of the related name. Clicking the new item will add automate adding the Related Names field to the related contact in the appropriate format (brother to sibling, father to child, spouse to spouse). Hopefully OS X 10.6 or OS 11 will include an improved Address Book which automatically does this, but Relationship Completer is the best solution at the moment.Full article.
(Hat tip: Leopard Tips)
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