create OUT: source refining IN: source;

helper context source!item def: doSomething() : source!item = 
		 self.refSetValue('interestingValue', 1)
;

helper context source!container def: generateSequence() : Sequence(source!item) =
	 self.group->iterate(e; res: Sequence(source!item) = Sequence{} |
		res->append(e.doSomething())
	)
;
	

rule putNewThingsThere {
	from
		s: source!container
	to
		t: source!container (
			group <- s.generateSequence()
		)
	}

rule duplicateItems {
     from
          i: source!item
     to
          i1: source!item(), // you don't modify the existing item
          i2: source!item ( // you create a duplicate of this existing item
              group <- i1.container, //assuming that you have a reference from an item to its container called "container"
              name <- i1.name
              //etc.
          )
}