Function sentences 

pub fn sentences(grants: &[Grant], labels: &dyn Labels) -> String

One sentence per grant, in the words of the person who gave it: where it applies, then what it answers for the kinds of action it covers.

describe merges a grant set into what each node finally answers; this keeps the grants apart, so a person reads the exception and the rule it narrows as the two records they are, and an agent handed the same sentences knows what it holds. Grants come from the most specific node to the least, so an exception sits beside the grant it excepts.