Clarify when Task.restriction can be used by adding text to the description:

either

1) clearly  restrict only to the current usage by adding to the currenet definition:

  "you can only use Task.restriction if the Task is for fulfillment of another request resource, and the restriction identifies what subset of the request is supposed to be fulfilled. A possible example could be a standing order (the request), and a single instantiation for fulfillment (the Task)."

and adding an invariant to restrict its usage to only when focus is present.

and adding to definition of Task.restriction.period: "is only used in relation to another request resource, specifically regarding request.occurrence[x] element. ( e.g., ServiceRequest.occurance[x] ).

OR 

2) loosen the definition to not require focus and provide a plain english description for Task.restriction.period to be able to express a notion  like "I need this done by next Friday" - that is to indicate that the request must be performed by a given point of time, after which the task is past the deadline and status either completed, failed, on-hold or cancelled ?