text:  /**~interaction~
   * InteractionFragment [Abstract Class]
   * 
   * Description
   * 
   * InteractionFragment is an abstract notion of the most general interaction unit. An InteractionFragment is a piece of an
   * Interaction. Each InteractionFragment is conceptually like an Interaction by itself.
   * 
   * Diagrams
   * 
   * Interactions, Lifelines, Occurrences, Fragments, Interaction Uses
   * 
   * Generalizations
   * 
   * NamedElement
   * 
   * Specializations
   * 
   * CombinedFragment, Continuation, ExecutionSpecification, Interaction, InteractionOperand, InteractionUse,
   * OccurrenceSpecification, StateInvariant
   * 
   * Association Ends
   * 
   *  covered : Lifeline [0..*] (opposite Lifeline::coveredBy)
   * 
   * References the Lifelines that the InteractionFragment involves.
   * 
   *  enclosingInteraction : Interaction [0..1]{subsets NamedElement::namespace} (opposite Interaction::fragment)
   * 
   * The Interaction enclosing this InteractionFragment.
   * 
   *  enclosingOperand : InteractionOperand [0..1]{subsets NamedElement::namespace} (opposite
   * InteractionOperand::fragment)
   * 
   * The operand enclosing this InteractionFragment (they may nest recursively).
   * 
   *  ♦ generalOrdering : GeneralOrdering [0..*]{subsets Element::ownedElement} (opposite
   * A_generalOrdering_interactionFragment::interactionFragment)
   * 
   * The general ordering relationships contained in this fragment.
  **/