anchor.diff:  ;
   // R710
   level3Expr : 
  -  (   level3Expr concatOp   )?   level2Expr
  +  level2Expr (   concatOp  level3Expr  )?
   ;
   // R711
   concatOp : 
  
positive.code: ;
  // R722
  expr : 
    (   expr definedBinaryOp   )?   level5Expr
  ;
  // R721
  equivOp : 
  
negative.code: // R913
  ioControlSpec : 
    (   UNIT  EQUALS    )?   ioUnit
  |   (   FMT  EQUALS    )?   fformat
  |   (   NML  EQUALS    )?   namelistGroupName
  | ADVANCE  EQUALS  scalarDefaultCharExpr
  | ASYNCHRONOUS  EQUALS  scalarCharInitializationExpr
  