+=item C<items>
+
+An optional array reference of RDBO instances for the items to use. If
+missing then the method C<items_sorted> will be called on
+C<$source>. This option can be used to override the sorting, to
+exclude certain positions or to add additional ones.
+
+=item C<skip_items_zero_qty>
+
+If trueish then items with a quantity of 0 are skipped.
+