"is a class to implement an `I'll get round to you when I can be bothered' scheduler. It's based on the queue system in our banks shops and some doctors I've been to. You turn up any time you want, but then you have to wait till everyone else who was there before you has been dealt with. The idea is to let the items being scheduled do so at any free time they wish and then worry about resource requirements later. If we can't handle some items when they were scheduled, they just queue until they can be handled."