I am familiar with Shelley Powers' work, having read Unix Power Tools, a book that holds a special place on my shelf for its usefulness and depth. She is obviously someone who knows what she is doing.
This book states in the preface that, "Readers of this book should be familiar with web page technology, including Cascading Style Sheets (CSS) and HTML/XHTML. Previous programming experience isn't required, though some sections may require extra review if you have no previous exposure to programming."
My first exposure to programming was in 1981, using BASIC on a Radio Shack TRS-80 Color Computer. Over the years, I have studied (and often forgotten, but can certainly read a bit and understand the concepts of) LISP, C, Bash scripting, Perl, Python, and more. Lately I have spent more time using PHP and enjoying it, since that is the language of things like Wordpress, Drupal, vBulletin and other commonly used CMS and interactive web site software. The two sentences quoted above seem perfectly clear to me, but I can imagine what they must seem like to someone with no experience with programming languages. So, now you have been warned. Let's get to the good stuff for those who understand the jargon.
This book is clear, with enough detail to help you understand what is happening without bogging you down in the minutiae. The reader is expected to see how and why each facet of the language would be useful, so the examples given are simple and seem to be designed to help the reader get the feel for usage without pretending to be a cookbook of programming recipes, although some seem quite useful as they are, such as Chapter 6's code for browser detection, which allows you to modify content and/or how it is displayed based on the web browser being used to view your site.