anchor.diff:  
   // --------------
   // Exception spec
  -
   throwsSpec
      : THROWS identifier (COMMA identifier)*
      ;
  
positive.code: labeledAlt
     : alternative (POUND identifier)?
     ;
  
  // --------------------
  // Lexer rules
  
  lexerRuleSpec
     : DOC_COMMENT* FRAGMENT? TOKEN_REF COLON lexerRuleBlock SEMI
     ;
  
  lexerRuleBlock
  
negative.code: lexerBlock
     : LPAREN lexerAltList RPAREN
     ;
     // E.g., channel(HIDDEN), skip, more, mode(INSIDE), push(INSIDE), pop
  
  lexerCommands
     : RARROW lexerCommand (COMMA lexerCommand)*
  