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Your code examples look nice to my eyes. You might want to post this on the gtk-perl maillist as other people are also working on tutorials and examples for Gtk3.
Before anyone gets too excited, Perl/Gtk3 is far from ready for use. The automatic documentaion generation of Gtk2, is no longer there. So there are NO docs for Perl. How are you going to expect people to work on something with no docs?
From Torsten Schoenfeld, the Perl Gtk3 leader:
There's indeed no Perl-specific documentation yet, and I'm not inclined to write it. All the necessary information is available on <http://developer.gnome.org/gtk3/stable/> and in the file "<prefix>/share/gir-1.0/Gtk-3.0.gir". A nice little project might be to write a viewer for all the information in the *.gir files (which include the actual documentation that ends up on developer.gnome.org). It could use Perl-specific syntax so people don't have to do the translation in their head. I definitely do not consider Gtk3 "finished" yet. We no doubt still miss quite a few overrides, and there are one or two low-level problems left.
You'd have to add Perl support. From the looks of it, you'd have to extend <http://git.gnome.org/browse/gobject-introspection/tree/giscanner/mallardwriter.py> to include a MallardFormatterPerl class and add mallard-Perl-*.tmpl files. You could most likely borrow heavily from the existing Python stuff.
> Does this mean for Perl, we would have to make an xml
That would be another option. Note that you don't have to write an XML parser yourself; there are lots on CPAN.