class SampleConfig(Config):
     composed_config1 = group_key(ChildConfig1)
     composed_config2 = group_key(ChildConfig2)
class ParentConfig(Config):
    prop1 = key('parent', 'PROP1')
    child_config = group_key(ChildConfig)
 class ParentConfig(Config):
     c1 = group_key(Child1)
     c2 = group_key(Child2)
class ChildConfig(Config):
    prop1 = key('child', 'PROP1')
    grandchild_config = group_key(GrandchildConfig)