in src/main/scala/com.gu.conf/impl/CompositeConfiguration.scala [31:35]
def getIdentifier = "composite[%s//%s]".format(primary.getIdentifier, secondary.getIdentifier)
def getPropertySource(propertyName: String): Option[AbstractConfiguration] = {
(primary getPropertySource propertyName) orElse (secondary getPropertySource propertyName)
}