This book is a brilliant reference book. If you want to see inside, go to amazon.com.
Don't be put off by the small size 15 x 23 x 1cm thick.
Very good quality paper, cream in colour, and very clear printing.
It covers most of the PHP functions you would probably ever want to use with a concise description and an example of its use.
Not for first time beginners, or those wanting to learn PHP.
You will need to know what you want to do in PHP, and have a reasonable idea of what the function might be.
So in short, it is a list of PHP functions sorted alphabetically in groups. Eg. Array functions, String functions, Date/Time functions etc.
The only down side is if a function has been depricated, it does not always tell you the alternative.
I find it far more helpfull than the official PHP reference found at php.net.