Most of those materials just discuss Perl's syntactic sugar which allows OO-style development. They offer very little in the way of wisdom about OO design.
Which is exactly what you'd expect from those pieces of documentation. OO design is language independent, and hence, you should expect material discussing OO design among the documentation discussing the syntax and features of a particular language.
If I buy a set of crayons, it might tell me how to open the package, and how to properly store them. It doesn't tell you how to produce art though.