Entered as: "The value -1 means that no hierarchy should be applied to a source field." (to mirror the language of the first sentence defining a hierarchy that is "applied to a source field."
Cleaned up the next paragraph a bit: To read:
If the data pilot source is provided by an external component or service, the data contained within category columns may be grouped by its valueand it may be further divided into sub-groups or hierarchies. If an external component supports hierarchies, it shall assign unique numbers to those hierarchies.
(We may want to think about the shall in that last sentence. I suspect what was meant was that if an external component supports hierarchies, it is responsible for assigning those hierarchies numbers if those are to be represented in the data pilot source. So, perhaps:
If an external component supports hierarchies it is responsible for the assignment of numbers that will preserve those hierarchies in a source field. (That's a guess on my part. If some can confirm I will enter it.)
Minor