I searched for this recently and the current set of questions and answers on stack overflow did have the answers but they were hard to find and so I felt they could be consolidated. This question is just about "window" tabs introduced in xcode 4, this question is ambiguous, and this question just seems to be about the library window.
There are now two types of tab in Xcode, "main" tabs along the top of the window and "sub" tabs within the editor areas within the window. What are the default keyboard shortcuts for switching / changing between them?