I just picked this up to try out GM'g a game for my son and his friends. I've seen several references (not just to this product, but elsewhere on the site) to "3.5," "3.5 conversion," and the "3.5 core rulebook." I'm confused by these references. I thought that Pathfinder RPG didn't revise their rules like D&D did... unless the 3.5 references are referring to how to play D&D characters with this module? Just trying to understand the difference between Pathfinder RPG and 3.5...? Thanks!