Refactored the default snippet dispatcher function to make it more likely that you won't have to override the whole thing for most cases. You can override the show, index, isShow and addCriteria methods individually (addCriteria was already there). The isShow method is used to decide if req.remainder is referring to an individual permalink page for a single snippet (a "show page") and, if so, should return the slug of the expected snippet. isShow is not responsible for finding out if the snippet really exists - dispatch will handle that for you and 404 if not.