Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Very in-depth

Quite a comprehensive guide to regular expressions. Gets very detailed in the areas that it covers. However, definitely not a 'beginner's guide'. I highly recommend that you are already comfortable with the basis of regular expressions before picking up this book. You will get way more out of it if this is not your first introduction to it. Comfort and proficiency with Perl would also be a big help. Title is correct though, this is a guide to 'mastering' regular expressions, not learning them from the beginning.