By core definition of XP methodology, there is a lack of design specification or documentations. Reference below is from Wiki - Extreme programming.
Critics have noted several potential drawbacks, including problems with unstable
requirements, no documented compromises of user conflicts, and a lack of an overall
design specification or document.
This approach has a number of critics and one of them:
Can increase the risk of scope creep due to the lack of detailed requirements documentation
Supporters of XP stress the following:
Coders like coding, not documenting, and coders like seeing code they've written work.
We are creating some documentation (UML snippets, method signatures and other remarks) and include some of them in unit tests. However, project have to document the code at some time, because it's how customers actually use those features that you thought up. It'd be selfish just to code and never document or comment on how the software works.
Any documentation is tough for a programmer since he can never explain the software in less than ten hundreds of words. Thus, option of having Video documents that records design approach and use cases, as well as diagrams to show interaction between components can be done with less time and more fun.