-If a price is set from a source, it is read only. A price edited manually is by
-definition not a sourced price.
+If a price is set from a source then the system will try to prevent the user
+from messing it up. By default this means the price will be read-only.
+Implementations can choose to make prices editable, but even then deviations
+from the calculatied price will be marked.
+
+A that is not set from a source will not have any of this.