Sets our main struct and passes it to the parent class.
This function creates a fraction GParamSpec for use by objects/elements that want to expose properties of fraction type. This function is typically used in connection with g_object_class_install_property() in a GObjects's instance_init function.
Get the main Gtk struct
the main Gtk struct as a void*
the main Gtk struct
A GParamSpec derived structure that contains the meta data for fractional properties.