statement on purpose of use should be stronger

Will update description to promote the benefit of being able to narrow the POU beyond TPO at the transaction level.   However, in regards to  "we would expect the purpose of use always be indicated for the task" Because this capability doesn’t really exist today – typically one overarching PoU defined at a business agreement level ( e.g. at app registration), we can't require it for every transaction. The current CDex design is flexible enough to support the current state of healthcare data and optionally provide additional granularity to define POU with a greater level of discrimination at the transaction level if and when it is implemented or required in the future.