anchor.diff:      ;
   
   nameAndTypeArguments
  -    : ( memberName | typeName ) 
  +    : ( memberName | typeName | 'subtype' ) 
         ( (typeArguments) => typeArguments )?
       ;
   
  
positive.code:         typeName
          typeParameters?
          caseTypes?
          satisfiedTypes?
          typeConstraints?
          interfaceBody
  
negative.code: 
  RETRY
      : 'retry'
      ;
  
  UNION
      : 'union'
      ;
  
  VOID
  