The proposal doesn't sound like that was what was intended - it seems like it is left to the user to implement the fibers, with the work priority to be set by the user somehow. Indeed, a quick glimpse of the commits of the implementation reveals a priority system of values exposed directly to the user when creating components (see unit tests).
acdlite is correct here -- most users won't need to worry about priorities and it's unclear to what extent we'll even expose them. The unit tests do not describe a public API (and we're not close to settling on one).
Thanks for the clarification! I've been flying 16 hours today (Milan to SF), so I'm sure I didn't grasp the full significance of the concepts in the doc.
