I bought this book for an intro to Theater class that requires the 11th edition. I figured I'd give saving some money a shot, then went through the chapters and compared the chapter titles with the chapter titles in the syllabus after classes started. Wouldn't you know it, they ended up being the same chapters with occasional renaming, but back one. For example, chapter four in the eleventh edition is the same as chapter three in this one. (Chapter 5, aka chapter 4 in the 10th edition, has a different title: "Stage Spaces" became "Theater Spaces.") Otherwise, from what I can tell, they're practically similar.
How did this happen, you ask? The introductory chapter in the tenth edition doesn't have a chapter number, and in the eleventh edition, it got one.