code: func addCollection(collection *Collection) {
  	for e := collections.Front(); e != nil; e = e.Next() {
  		otherCollection := e.Value.(*Collection)
  		if collection.spec.typ == otherCollection.spec.typ {
  			// The Collection was already added to the list. No need to do
  			// anything.
  			return
  		}
  	}
  	collections.PushFront(collection)
  }
docs: // addCollection adds the given spec to the list of collections iff it has not
  // already been added.