anchor.diff:   : '('  balanced_tokens? ')'
    | '[' balanced_tokens? ']'
    | '{' balanced_tokens? '}'
  - | identifier | expression | context_sensitive_keyword | literal | operator
  + | (identifier | context_sensitive_keyword | literal | operator)+
  + | expression
   // | Any punctuation except ( ,  ')' , '[' , ']' , { , or } TODO add?
    ;
   
  
positive.code: 
  parenthesized_expression : '(' expression_element_list? ')'  ;
  expression_element_list : expression_element (',' expression_element)* ;
  expression_element : expression | identifier ':' expression  ;
  
  // GRAMMAR OF A WILDCARD EXPRESSION
  
  
negative.code: /*
   * alexsaveliev: added comma-separate tokens to support
   * @available(*, unavailable, message="Please wrap your tuple argument in parentheses: 'print((...))'")
   * alexsaveliev: multiple identiiers/literals in a row to support "@available(iOS 9.0, OSX 10.11, *)"
   */
  balanced_tokens
   : balanced_token+
  