In the first issue of "XP Explained" there were twelve practices.
In the second edition, the practice was reorganized: some of them were renamed or merged, some of them were deleted (metaphor), and now there are thirteen primary and eleven investigative actions.
In the "Practice of the First Edition" section of the page, you can find an initial list of twelve practices and how they appear in the update.
While reading, you will certainly distinguish between XP and XP2e (second edition of XP).
Most likely, the first edition had four principles, and the second option (Respect) was presented in the second edition.
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