The current MessageHeader profile description reads:

PAO MessageHeader Resource Profile This profiles is used to order, update, cancel and query the status of an order It requires the consistant use of identifiers to ensure that any actions targeted at a prior order affectonly that order.

But there are several typos and it should probably read:

This profile is used to order, update, cancel and query the status of an order*.* It requires the consistent use of identifiers to ensure that any actions targeted at a prior order affect only that order.