Many XML developers, just when they've gotten used to DTDs, are hearing about alternatives and wondering what to do with them. W3C schemas, RELAX NG, Schematron -- which should they go with? What will each buy them? What software support does each have? How much of their current systems will they still be able to use? The feeling of unease behind these questions can be summed up with one question: if I leave DTDs behind to use one of the others, will I regret it?