A #PeasEngine, or %NULL.
the extension #GType.
the name of the first property.
the value of the first property, followed optionally by more name/value pairs, followed by %NULL.
Return: a new instance of #PeasExtensionSet.
ConstructionException GTK+ fails to create the object.
Create a new #PeasExtensionSet for the @exten_type extension type.
If @engine is %NULL, then the default engine will be used.
See peas_extension_set_new() for more information.