code: function placeForTarget( targetOrPlaceId, place = activePlace ) {
        let placeId = place ? place.targets[ targetOrPlaceId ] : null;
        if( placeId == null ) {
           placeId = targetOrPlaceId;
        }
        assert.state(
           placeId in availablePlaces,
           `Unknown target or place "${targetOrPlaceId}". Current place: "${place.id}"`
        );
        return availablePlaces[ placeId ];
     }
docs: ///////////////////////////////////////////////////////////////////////////////////////////////////////// 
  Get the place definition for a given target or place. If the provided identifier is a target of the
  current place, the definition of the referenced place is returned. Otherwise, the current place is
  returned.
  
  @param {String} targetOrPlaceId
  a string identifying the target or place to obtain a definition for
  @param {Object} place
  the corresponding place definition
  
  @return {Object}
  a place definition with `targets` and `patterns` as specified in the flow definition, plus `id`