Perl is without doubt one of the most complex languages in wide use today - even C++ arguably seems simple in comparison, while Java, C#, Python, etc are a snap. In the past there has been a strong tendency for writers of introductory books to deal with this complexity by leaving important features out. Worse, for marketing reasons they often don't tell readers they have done this.
This makes writing much easier, but can mean readers can finish books as bad or even dangerous programmers. (For instance if you learned Perl from Randall Schwartz's "Learning Perl", you not only wouldn't be able to write a function that could add two lists of numbers, but you wouldn't know that you didn't know this, and wouldn't know what was going on when you tried..)
By comparison, this text (part of a series editted by the legendary Scott Meyers, author of "Effective C++") is exemplary. It is both thorough and clear, giving crystal clear explanations of all Perl's major features, including arguably the best introduction to regular expressions anywhere, and covering superbly the essential but tricky subject of references (one of the things introductions often drop).
While thorough enough to suit the professional programmer, TYP24H is also clear and friendly enough to be used as in an introduction to Perl by first time programmers.
A truly superb achievement - I'm horribly envious!