Regenerate: Regeneration is a destruction-replacement effect. "Regenerate [permanent]" means "The next time [permanent] would be destroyed this turn, instead remove all damage from it, tap it, and (if it's in combat) remove it from combat." Because it's a replacement effect, it must be active before the attempted destruction event. Abilities that trigger from damage being dealt still trigger even if the permanent regenerates. See rule 419.6b. (Rules Version Date: February 1, 2005. See
http://www.wizards.com/magic/comprules)