anchor.diff:  availability_argument : Platform | '*' ;
   
   /** Must match as token so Platform_version doesn't look like a float literal */
  -Platform : Platform_name WS? Platform_version ;
  +// alexsaveliev: replaced Platform_name with identifier
  +// testcase: #elseif os(Linux)
  +Platform : Identifier WS? Platform_version ;
   
   fragment
   Platform_name
  
positive.code: 
  // GRAMMAR OF A CLASS DECLARATION
  
  class_declaration
   : attributes? access_level_modifier? 'class' class_name
     generic_parameter_clause? type_inheritance_clause? class_body
   ;
  class_name : identifier ;
  class_body : '{' declarations? '}'  ;
  
  
negative.code: 
  // GRAMMAR OF AN EXTENSION DECLARATION
  
  /*
   * alexsaveliev: added requirement_clause? to support
   * "extension TypeIndexed where Value : ForwardIndexType ..."
   * see http://www.raywenderlich.com/109156/introducing-protocol-oriented-programming-in-swift-2
   */
  extension_declaration : access_level_modifier? 'extension' type_identifier requirement_clause? type_inheritance_clause? extension_body  ;
  extension_body : '{' declarations?'}'  ;
  
  // GRAMMAR OF A SUBSCRIPT DECLARATION
  