Note: Nonoccurrence features that should be vars (including "top-level" features) require a constraint on occurrences to make them var.
  
Readonly features (must be vars)
    
    Links::Link:participant:Anything[2..*] nonunique ordered;
    Links::BinaryLink::source/target: Anything[0..*] nonunique subsets participant;
      Another data point for the JIRA discussion on participants as (non) vars.

    Metaobjects::Metaobject::annotatedElement:Element[1..*]
    Metaobjects::SemanticMetadata::redefines annotatedElement : Type[1]

    Clocks::universalClock:UniversalClockLife[1]
    Observation::defaultMonitor[1] : DefaultMonitorLife
    SpatialFrames::feature defaultFrame : DefaultFrameLife[1]
      Above are domain Anything ("top level").
      Must be const to prevent deleting the (single) *Life, then immediate recreating and "resetting" feature (logically possible).            

  Readonly on occurrence features:  

    Transfers::Transfer:isInstant/isMove/isPush: Boolean[1]
    StatePerformances::StatePerformance:incomingTransitionTrigger : MessageTransfer [0..1] default null

"Root" features on non-occurrences, all "top-level" (intended to "change" over time)

  Base::things: Anything [1..*] nonunique
  Base::dataValues: DataValue[0..*] nonunique subsets things
  Base::naturals: ScalarValues::Natural[0..*] subsets dataValues
  
  Could these change dynamically?
  Base::zeroOrOne [0..1]  (multiplicity)
  Base::oneToMany [1..*]  (multiplicity)
  Base::zeroToMany [0..*] (multiplicity)

  Links::links: Link[0..*] nonunique subsets things
  Links::binaryLinks: BinaryLink[0..*] nonunique subsets links
  Links::selfLinks: SelfLink[0..*] nonunique subsets binaryLinks

  Could these change dynamically?  
  Metaobjects::feature metaobjects : Metaobject[0..*] :> objects

  Occurrences::occurrences: Occurrence[0..*] nonunique subsets things;
  Occurrences::earlierFirstIncomingTransferSort : IncomingTransferSort 

  Objects::objects: Object[0..*] nonunique subsets occurrences {
  Objects::linkObjects: LinkObject[0..*] nonunique subsets links, objects intersects links, objects {
  Objects::binaryLinkObjects: BinaryLinkObject[0..*] nonunique subsets binaryLinks, linkObjects

  Performances, Transfers:: Assuming these top-level steps, exprs,
    transfers, flows are non-vars (at least for steps, transfers, and
    flows, since theire specializations will be linked by
    successions).