nsIEnumerator Interface

 CurrentItem will return the CurrentItem item it will fail if the 
  list is empty

nsISupports currentItem()

 First will reset the list. will return NS_FAILED if no items

void first()

 return if the collection is at the end.  that is the beginning following 
  a call to Prev and it is the end of the list following a call to next

void isDone()

 Next will advance the list. will return failed if already at end

void next()