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    Some software packages install loadable GTK+ modules such as theme engines,
    gdk-pixbuf loaders or input methods. Since GTK+ 3 is parallel-installable
    with GTK+ 2.x, the two GTK+ versions have separate locations for their
    loadable modules. The location for GTK+ 2.x is
    libdir/gtk-2.0libdir/gtk-3.0
    For some kinds of modules, namely input methods and pixbuf loaders,
    GTK+ keeps a cache file with extra information about the modules.
    For GTK+ 2.x, these cache files are located in
    sysconfdir/gtk-2.0libdir/gtk-3.0/3.0.0/
Note that GTK+ modules often link against libgtk, libgdk-pixbuf, etc. If that is the case for your module, you have to be careful to link the GTK+ 2.x version of your module against the 2.x version of the libraries, and the GTK+ 3 version against hte 3.x versions. Loading a module linked against libgtk 2.x into an application using GTK+ 3 will lead to unhappiness and must be avoided.