I read the custom components chapter in this book to beef up my knowledge, having completed a few tutorials on creating Spark components already (thank goodness I had!) The author, rather than building up a single simple example has decided to show 'component code' for one component, but 'skin code' from some other component (actually he refers back to an earlier code example, as if creating a single cohesive example for this chapter was too much trouble).
Furthermore the skin code example has been unnecessarily imported from Adobe Illustrator (there is no actual end-component example to accompany this chapter, so why do that?)- all it means is that the example code contains additional Illustrator-specific information which in most circumstances is not needed, and it is not even explained here despite this supposedly being an introduction to Flex4 and Spark components.
The example also seems incomplete as there is no specific discussion about declaring the states-node in the skin-part to correspond with the component code. The first part of the chapter ends with the words "You now know how to make a simple custom component. Next up are composite components". Trust me, if all you have read is this chapter you won't know how, and you probably shouldn't proceed.
This book gets STUNNING reviews on Amazon.com but look deeper and almost all reviewers have either only reviewed this book, or have largely only reviewed other Manning publications - apart from someone who only gives it a 2 star review and says that the Spark info in this book is sadly lacking - possibly the only honest review there!
Having said that, a few chapters in this book are good - if you want to learn RobotLegs then Joel Hook's chapter is a great read, but otherwise I would steer clear. I'm sure all the authors are knowledgable but had unrealistic pressure to get something completed in too-short a time. This book certainly doesn't appear to have been peer-reviewed properly and is far too verbose in places .... and shame on any publisher who reviews their own books rather than striving to produce something of better quality (if indeed that is what's happened here - but I'll leave you to check out the reviewers' profiles and decide for yourself).