Dark Ages is an expansion for Dominion built around the theme of trashing cards.
Dark Ages is the largest dominion expansion, adding 35 new kingdom cards in addition to new "bad" cards, which are somewhere between Estates and Curses. Its central theme is trashing, so it includes cards that have abilities that activate when trashed or that interact with the trash in some way.
The Dominion rules are extraordinarily comprehensive. For questions regarding how cards interact, if you can, check the individual card entries in the appropriate rulebook(s) and you'll probably find your answer there. A PDF of the Dominion: Dark Ages rules is available here.