The book is useful but does not provide much new info for me. It spells a few things out clearly that are otherwise hard to figure out, with line-by-line code walkthrough.
Here are a few of the gaps:
I liked the section on XML Schemas, since I didn't know anything about them. I can't say that the book helped with today's particular problem of interest.
Trying SAX Modules
Installed Pod::SAX with cpan. This has many dependencies, including XML::SAX::Writer. Installed okay. Pod documentation for the functions is missing. This style of code doesn't look like the kind of code that I like write.
Installed XML::Generator::DBI with cpan. It failed tests looking for DBD/Pg.pm, there is some manual configuration that needs to be done. I didn't pursue this further because I have no database on this machine. The code is interesting to read though, both as an example of using XML::Handler::YAWriter and a nifty flexible DBI query.
I installed psh and fooled around with it. It looks like fun, but possibly dangerous since I don't know what I'm doing. My shell needs to be very reliable, eg rm commands.
I installed File::List, and wrote and example program using File::Flat with it. I posted this snippet as an answer to a question at perlmonks.