From the book Mastering Regular Expressions, 3rd Edition:
The story that is the first six chapters form the basis for the last four, covering specifics of Perl, Java, .NET, and PHP. To help you get the most from each part, I've used cross references liberally, and I've worked hard to make the index as useful as possible. (Over 1,200 cross references are sprinkled throughout the book; they are often presented as --> followed by a page number.)
I can't make grammatical sense of the first sentence. It seems that the subject is the story. The rest reads that is the first six chapters form the basis for the last four, covering specifics of Perl, Java, .NET, and PHP and seems to be a dependent clause. But where is the subject's verb? ...actually, the sentence is very confusing.