+=item C<call_sub $name, @args>
+
+Calls the sub C<$name> on C<$self> with the arguments C<@args> and
+returns its result. This is meant for situations in which the sub's
+name is a composite, e.g.
+
+ my $chart_id = $buchungsgruppe->call_sub(($is_sales ? "income" : "expense") . "_accno_id_${taxzone_id}");
+