+The current model of price sources requires a record and a record_item for
+every price calculation. This means that price structures can never be used
+when no record is available, such as calculation the worth of assembly rows.
+
+A possible solution is to either split price sources into simple and complex
+ones (where the former do not require records).
+
+Another would be to have default values for the inpout normally taken from
+records (like qty defaulting to 1).
+
+A last one would be to provide an alternative input channel for needed
+properties.
+
+=item *
+
+Discount sources were implemented as a copy of the prices with slightly
+different semantics. Need to do a real design. A requirement is, that a sinle
+source can provide both prices and discounts (needed for price_rules).
+
+=item *
+
+Priorities are implemented ad hoc. The semantics which are chosen by the "best"
+accessors are unintuitive because they do not guarantee anything. Better
+terminology might help.
+
+=item *
+
+It is currently not possible to link a price to the price of the generating
+record_item (i.e. the price of a delivery order item to the order item it was
+generated from). This is crucial to enterprises that calculate all their prices
+in orders, and update those after they made delivery orders.
+
+=item *
+
+Currently it is only possible to provide additional prices, but not to restrict
+prices. Potential scenarios include credit limit customers which do not receive
+benefits from sales, or general ALLOW, DENY order calculation.
+
+=item *
+
+Composing price sources is disallowed for clarity, but all price sources need
+to be aware of units. This is madness.
+
+=back