RSS settings: What does "remove articles" mean

In DT3’s preferences, I can choose to “Remove articles” after (e.g.) 1 week. What exactly does that mean – are the articles moved to the trash or removed completely?

In the first case: Is there a way to empty the feed’s trash automatically? I didn’t see a way to select the trash in the smart rules “search” options …

They’re trashed. However, since version 3 you could disable this option and use smart rules to get rid of old news.

Like so?