Frederic Marand has pointed out a new subversion repository that's been set up for the documentation on the PHP-GTK project.
After recent complaints in the PHP-GTK mailing list, auroraeosrose mentioned mgdm has set up a SVN repository for the docs, to ease working on them. This new repository is available at http://svn.thefrozenfire.com/phpgtkdoc/
The trunk currently has repositories for the gtkdocs and the phpdoc application you can check out and use to generate and develop on the documentation locally.