Write a comment about questions in this movement group.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@25469 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/QuantitySignMovementGroup.py

 ##############################################################################
 #
-# Copyright (c) 2008 Nexedi SA and Contributors. All Rights Reserved.
+# Copyright (c) 2008,2009 Nexedi SA and Contributors. All Rights Reserved.
 #
 # WARNING: This program as such is intended to be used by professional
 # programmers who take the whole responsibility of assessing all potential
@@ -25,6 +25,26 @@
 #
 ##############################################################################
 
+r"""
+Quantity Sign Movement Group is used to separate movements based on
+the signs of the quantities.
+
+This is probably used only in erp5_immobilisation. But this implementation
+has a serious problem that the quantity sign is not set in a movement,
+if the movement is created manually, because only this movement group
+set that property with a builder. So a builder always creates new movements,
+even if simulation movements match existing movements.
+
+This is not easy to fix, because nobody available knows how this is supposed
+to work precisely. In addition, it is questionable even that this movement
+group makes sense. From accounting point of view, if the same account is
+used, there is no problem in merging debits and credits.
+
+So somebody must consult the spec of immobilisation accounting, and the
+implementation of erp5_immobilisation seriously, to understand why and
+whether this is really required.
+"""
+
 from Products.ERP5.Document.MovementGroup import MovementGroup
 
 class QuantitySignMovementGroup(MovementGroup):