I guess I should start by saying that I'm not all that satisfied with any of the three popular computer books that I've bought. Learning Perl is one of those three.
Among the things that could be improved is the section on numeric operators, p. 22, where it says "In addition, there are other numeric operators, which we'll introduce as we need them." Even the index only lists p. 22 under operators, numeric. Page 32 contains a more complete listing of operators. This is one of the many notes I made in the index.
Similarly, p. 117 says "There are many other option modifiers available. We'll cover those as we get to them..." A few documentation references are given, but not perlre.
Among the other additions and notes I made in the index are:
"Modifiers--see option modifiers on p. 116-117,"
I mainly use the index, but I also made a note in the contents--under chapter 9. Using Regular Expressions, I wrote "see p.239," where there is more regex information (chapter 17).
I made numerous notes in the Symbols section of the index, such as listing page 240 next to the question mark, so I'll be referred to the non-greedy quantifier. The only page the book refers me to for the question mark is 101, which is about the "preceding item is optional" use of the question mark. Other notes were made for the vertical bar (see pipe, p.303), and the range operator (see p. 43).
There are other notes scattered through the book. I have no better beginner's Perl book to recommend, but Learning Perl needs some work.