However, having scanned this chapter, you'll know they exist, where to get more info about them and what they'll tell you when you use them. More prosaically, the chapter ends with a discussion of other more traditional Domino server commands that any serious developer should be aware of.
The rest of the book is much more a developer's reference. To get the best from it, you should be sure that you download the sample databases from IBM Press. Indeed, they appear to be available to anyone who goes to the book's page on the web site. The key is the ISBN 10 digit number: 0132943050.
The last few pages are on client-side debugging techniques, always useful.
It also discusses the functions you use to get hold of controls on the page and program them. There's also a section on interfacing with Java via the Domino Java design element in 8.5.3 and beyond.
Chapter Six is definitely worth a read if you are actively working on an XPages project. It's all about server-side debugging techniques.
Having myself been part of an extensive XPages project back in the 8.5.0 and 8.5.1 era, I know just how painful this was then. It still is somewhat painful, as there is no SSJS debugger, but this chapter shows you some techniques for overcoming this shortfall which you will find useful.
Read it before you start coding, and then re-read the piece on client side debugging in Chapter Four again.
The book comes in two versions, paper, which is what I reviewed from, and as an ebook -- or you can have both as a bundle. Personally, for reference of this sort, I prefer paper, because I can read with one eye and type with the other, but your preference may be different. You choose.
But is the $21.95 book worth buying?
Any reference book lives or dies by your ability to find what you need in it easily -- which means it needs to be indexed well, in the paper version, and searchable in the ebook version.
The paper one has three indexes: there's one printed inside the outer covers, as an "I want to do" list of about 80 headings. The contents pages are pretty well detailed, but they do require that you have some idea of what you are looking for and where in the book it's likely to be.
There's also an index at the back, running to 10 pages. Of course, unusual for most books but realistic in this one, the letter "X" has nearly 4 pages to itself. These indexes between them mean that finding stuff in the paper edition isn't too difficult.