anchor.diff:      :   hierarchical_function_identifier attribute_instance*
           '(' (expression ( ',' expression )*)? ')'
       ;
  -system_function_call : system_function_identifier ( (expression ( ',' expression )*)? )? ;
  +system_function_call : system_function_identifier (expression ( ',' expression )*)? ;
   genvar_function_call : genvar_function_identifier attribute_instance*
                          '(' (constant_expression ( ',' constant_expression )*)? ')'
   ;
  
positive.code: default_clause : 'default' ;
  inst_clause : 'instance' inst_name ;
  inst_name : topmodule_identifier ( '.' instance_identifier )* ;
  liblist_clause : 'liblist' ( ( library_identifier )* )? ;
  cell_clause : 'cell' ( library_identifier '.' )? cell_identifier ;
  use_clause : 'use' ( library_identifier '.' )? cell_identifier ( ':config' )? ;
  
  
negative.code: // 9.4 Identifier branches
  
  simple_hierarchical_branch :
  	Simple_identifier ( '[' Decimal_number ']' )?
   	( '.' Simple_identifier ( '[' Decimal_number ']' )? )*
  ;
  
  escaped_hierarchical_branch :
  	Escaped_identifier ( '[' Decimal_number ']' )?
  	( '.' Escaped_identifier ( '[' Decimal_number ']' )? )*
  ;
  
  // 9.5 White space
  