Hi, I have some questions/feedback on the candidate FHIR Tasks Resource (http://hl7.org/fhir/2016May/task.html). Is this the appropriate place for such feedback or is it better placed on the chat (https://chat.fhir.org/)?
To start off with something simple it seems that the TaskStatus is missing the cancelled state that is implied by the $cancel operation (http://hl7.org/fhir/2016May/task-operations.html#cancel).
Regarding the Task State Machine it would be helpful to have a diagram of the state machine 
But I also wonder if it is appropriate to have Completed and Cancelled as terminals. As the state of a task will mostly be controlled by user input, it seems appropriate to allow the user to revert any accidental state changes eg press cancel instead of complete in the UI, marked the wrong task as complete. I would have thought a $reopen operation that moved the state of the task back to the ready state is necessary.
Tasks are often presented in a list (eg “My Tasks”, “Outstanding Tasks for Patient X”) so I wonder if it is sensible to include a title string field as well as the description? As the description could potentially be a large wall of text. This would allow a user interface displaying a list of tasks to have an easy way of to display a compact display of a task.
The task resource does not currently have a concept of a due date which seems important to me. Most activities are time sensitive to some degree, whether it effects the patient’s condition eg redress wounds, administer medicine, or because of scheduling/workflow eg radiology report required before follow-up appointment, or simply so the patient feels that their care is progressing at a reasonable rate.
Some task systems record the person who completed the task and when it was completed. For a FHIR task with status completed does the owner and lastModified represent the person completing and time of completion?
Thanks
Rowan