Section A.1.3, and its excerpts in Syntax 3-5, Syntax 11-1
Module and primitive source text (Classes)

REPLACE

class_declaration ::=

{ attribute_instance } [ virtual ] class [ lifetime ] class_identifier [ parameter_port_list ]

[ extends class_identifier ] ; [ timeunits_declaration ] { class_item }

endclass [ : class_identifier ]

WITH

class_declaration ::=

{ attribute_instance } [ virtual ] class [ lifetime ] class_identifier [ parameter_port_list ]

[ extends class_identifier [ parameter_value_assignment ] ] ;

[ timeunits_declaration ] { class_item }

endclass [ : class_identifier ]