I propose some minor tightening-up of the spec for fn:random-number-generator:

(a) In the phrase "the keys of any such entries should start with an underscore character", give "should" RFC2119 markup.

(b) The two returned functions (the 'permute' function and the 'next' function) are somewhat informally described. We should be explicit about the function signature, name, and arity of each function as well as describing its effect:

next: 
  name: absent
  parameter names: ()
  signature: () => map(xs:string, item())
  implementation: as described in prose
  non-local variable bindings: none

permute:
  name: absent
  parameter names: ("arg")
  signature: (item()*) => item()*
  implementation: as described in prose
  non-local variable bindings: none


(I've given the argument of permute a name, because for some reason the data model says that function arguments have names, even though there is no way of writing a query that makes use of the fact).