The GTK+ module is designed to be loaded using gnome-settings-daemon by the
gnome-packagekit package.
It can however be launched for testing using:
GTK_MODULES="$GTK_MODULES:/usr/lib/gtk-2.0/modules/pk-gtk-module.so" application
The module installs a custom default pangocairo font map during gtk_init().
Pango will then call back with any languages which need installing, and these
are queued up. In an idle callback these are emitted as an asyncronous D-BUS
method to the session PackageKit InstallFonts() method.
If configured to do so, this will prompt the user to install new fonts.
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