+=item C<linked_invoices>
+
+Returns an array of record objects (invoices, debit, credit or gl objects)
+which are linked for this bank transaction.
+
+Returns an empty array ref if no links are found.
+Usage:
+ croak("No linked records at all") unless @{ $bt->linked_invoices() };
+
+
+=item C<not_assigned_amount>
+
+Returns the not open amount of this bank transaction.
+Dies if the return amount is higher than the original amount.
+
+=item C<closed_period>
+
+Returns 1 if the bank transaction valutadate is in a closed period, 0 if the
+valutadate of the bank transaction is not in a closed period.
+