sub myfunction {
	my %defs = ( optionA=>2e6, optionB=>'defA', optionC=>'defB' );
	my %user = ( %defs, @_ );
	my %opts; @opts{keys %defs} = delete @user{keys %defs};
	carp "Unknown options: '@{[ %user ]}' ignored." 
          if %user;
     # %opts user known user supplied options
     # defaults for unsupplied options
     # Warning issued about unknown options
     # do stuff.
}