Okay, I know that there is some way to do this, but I'm stuck. My question is for an end-user subscribing to a classified ad RSS feed. What I want is for my desktop widget to be notified whenever a listing appears in the feed with a search keyword---in this case, "mac". I want to know whenever a Mac appears for sale in my local listing. I have the feed, and I'm subscribed to it, but how can I arrange to receive an e-mail for new listings only which contain my keyword?