anchor.diff:  
   filename
   	: STRING
  +	| variable_identifier
   	;
   
   // 17.4 Simulation control system tasks
  
positive.code: 	: DOLLAR_DUMPPORTSLIMIT LEFT_PARENTHESIS file_size COMMA file_pathname RIGHT_PARENTHESIS SEMICOLON
  	;
  
  file_size
  	: DECIMAL_NUMBER
  	;
  
  // 18.3.5 Reading dump file during simulation ($dumpportsflush)
  
  dumpportsflush_task
  	: DOLLAR_DUMPPORTSFLUSH LEFT_PARENTHESIS file_pathname RIGHT_PARENTHESIS SEMICOLON
  	;
  
  // 18.4 Format of extended VCD file
  // 18.4.1 Syntax of extended VCD file
  
  value_change_dump_definitions
  	: declaration_command* simulation_command*
  	;
  
  declaration_command
  	: declaration_keyword COMMAND_TEXT? DOLLAR_END
  	;
  
  simulation_command
  	: simulation_keyword VALUE_CHANGE* DOLLAR_END
  	;
  
  declaration_keyword
  	: DOLLAR_COMMENT
  	| DOLLAR_DATE
  	| DOLLAR_ENDDEFINITIONS
  	| DOLLAR_SCOPE
  	| DOLLAR_TIMESCALE
  	| DOLLAR_UPSCOPE
  	| DOLLAR_VAR
  	| DOLLAR_VCDCLOSE
  	| DOLLAR_VERSION
  	;
  
  simulation_keyword
  	: DOLLAR_DUMPPORTS
  	| DOLLAR_DUMPPORTSOFF
  	| DOLLAR_DUMPPORTSON
  	| DOLLAR_DUMPPORTSALL
  	;
  */
  // A.1 Source text
  // A.1.1 Library source text
  
  
negative.code: 	;
  
  file_pathname
  	: STRING
  	| variable_identifier
  	| expression
  	;
  
  // 18.3.2 Stopping and resuming the dump ($dumpportsoff/$dumpportson)
  