anchor.diff:  options { tokenVocab = ANTLRv4Lexer; }
   // The main entry point for parsing a v4 grammar.
   grammarSpec
  -   : DOC_COMMENT* grammarDecl prequelConstruct* rules modeSpec* EOF
  +   : grammarDecl prequelConstruct* rules modeSpec* EOF
      ;
   
   grammarDecl
  
positive.code: grammarType
     : (LEXER GRAMMAR | PARSER GRAMMAR | GRAMMAR)
     ;
  
  // This is the list of all constructs that can be declared before
  // the set of rules that compose the grammar, and is invoked 0..n
  // times by the grammarPrequel rule.
  
  prequelConstruct
     : optionsSpec
  
negative.code: labeledAlt
     : alternative (POUND identifier)?
     ;
     // --------------------
     // Lexer rules
  
  lexerRuleSpec
     : FRAGMENT? TOKEN_REF COLON lexerRuleBlock SEMI
     ;
  
  lexerRuleBlock
  