You're the owner of an XP project. You need a document - say, a UML diagram of the main classes to show your boss. How do you get it?
How do you get anything on an XP project? Well, duh. You write a UserStory that says "Draw UML diagrams of the main classes in the system." Schedule it in the next iteration. A developer signs up for the story, draws the diagram.
Next question?
How do you estimate a task that nobody has any real familiarity with? Assuming that no-one has done a UML diagram of a part of the system yet? Would this be a candidate for a SpikeSolution, or would you allow for the fact that this job might overrun?
You have to either estimate it and try to live by the estimate, or spike it. What C3 will do when we have to do this, if I have my way, will be to bring in MartinFowler to teach his wonderful course on UmlDistilled, and to hang about a couple of days coaching us on what to document and what not. -- RonJeffries