anchor.diff:  		expr
   	|	ac-implied-do
   	;
  +	ac-value-list :
  +		ac-value ( ',' ac-value ) *
  +	;
   
   /*
   	R473 ac-implied-do is ( ac-value-list , ac-implied-do-control )
  
positive.code: 	|	IOMSG '=' iomsg-variable
  	|	IOSTAT '=' scalar-int-variable
  	;
  
  /*
  	R924 backspace-stmt is BACKSPACE file-unit-number
  
negative.code: 	ACTION : 'ACTION' ;
  	ALLOCATABLE : 'ALLOCATABLE' ;
  	ALLOCATE : 'ALLOCATE' ;
  	AND : 'AND' ;
  	ACQUIRED_LOCK : 'ACQUIRED\\s+LOCK' ;
  	ADVANCE : 'ADVANCE' ;
  	ASSOCIATE : 'ASSOCIATE' ;
  	ASYNCHRONOUS : 'ASYNCHRONOUS' ;
  	BACKSPACE : 'BACKSPACE' ;
  	BIND : 'BIND' ;
  	BLANK : 'BLANK' ;
  	BLOCK : 'BLOCK' ;
  