说明：  这本书介绍了xp背后的思想——它的根源、哲学、情节等。它将帮助读者选择是否在项目中使用xp时做出明智的决策。本书的另一个目的是帮助那些已经在使用 xp的读者更好地理解它。
(This book describes xp behind the idea- it' s roots, philosophy, plot. It will help readers to choose whether to use in the project xp make informed decisions. Another purpose of this book is to help those who are already in use xp readers a better understanding of it.)