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: // 9 General
  // 9.1 Attributes
  
  attribute_instance : '(*' attr_spec ( ',' attr_spec )* '*)' ;
  attr_spec : attr_name '=' constant_expression
  | attr_name
  ;
  
negative.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' )? ;
  
  