anchor.diff:          satisfiedTypes?
           typeConstraints?
           classBody
  -    ;
  -
  -unionDeclaration
  -    :
  -        'choice'!
  -        typeName
  -        typeParameters?
  -        caseTypes
  -        satisfiedTypes?
  -        typeConstraints?
  -        ';'
       ;
   
   objectDeclaration
  
positive.code:     -> ^(ALIAS_DECL aliasDeclaration)
      | objectDeclaration
      -> ^(OBJECT_DECL objectDeclaration)
      | unionDeclaration
      ;
  
  importDeclaration
  
negative.code:     :   'break'
      ;
  
  CASE
      :   'case'
      ;
  