The organising system is meant to be the prefixes - unfortunately, as often as not, people dom't use these.

Like freda, I prefer rummaging around. The same way I prefer bookshops and libraries where everything is fairly muddled up together, rather than where everything is organised, sometimes in ways that don't really help. For example, when they break up the fiction into categories - I once saw a shelf marked "Romance" which had Wuthering Heights and Pride and Prejudice alongside Barbara Cartland.