anchor.diff:  attribute : '@' attribute_name attribute_argument_clause? ;
   attribute_name : identifier  ;
   attribute_argument_clause : '('  balanced_tokens?  ')'  ;
  -attributes : attribute attributes? ;
  -balanced_tokens : balanced_token balanced_tokens? ;
  +attributes : attribute+ ;
  +balanced_tokens : balanced_token+ ;
   balanced_token : '('  balanced_tokens? ')'
  - | '[' balanced_tokens?']'
  - | '{' balanced_tokens?'}'
  + | '[' balanced_tokens? ']'
  + | '{' balanced_tokens? '}'
    | identifier | expression | context_sensitive_keyword | literal | Operator
   // | Any punctuation except ( ,  ')' , '[' , ']' , { , or }
    ;
  
positive.code: 
  // GRAMMAR OF A TYPE IDENTIFIER
  
  type_identifier : type_name generic_argument_clause? type_name generic_argument_clause? '.' type_identifier  ;
  type_name : identifier  ;
  
  // GRAMMAR OF A TUPLE TYPE
  
negative.code: // GRAMMAR OF A STRING LITERAL
  
  String_literal : '"' Quoted_text '"' ;
  fragment Quoted_text : Quoted_text_item Quoted_text? ;
  fragment Quoted_text_item : Escaped_character
  // | '\\(' expression ')'
   | ~["\\\u000A\u000D]
   ;
  