Add some details about the hostrange() function

The documentation of the behavior and formats of arguments needs
to be as precise as possible.

Ticket: CFE-3104

reference/functions/hostrange.markdown

@@ -7,11 +7,18 @@ tags: [reference, communication functions, functions, hostrange]
 
 [%CFEngine_function_prototype(prefix, range)%]
 
-**Description:** Returns whether the current host lies in the `range` of
-enumerated hostnames specified with `prefix`.
+**Description:** Returns whether the unqualified name of the current host lies
+in the `range` of enumerated hostnames specified with `prefix`.
 
 This is a pattern matching function for non-regular (enumerated)
-expressions.
+expressions. The `range` specification is in the format `A-B` (using a minus
+character `-`) where `A` and `B` are decimal integers, optionally prefixed with
+zeroes (e.g. `01`). The unqualified name of the current host used in this
+function is the same as the contents of the [`sys.uqhost`][sys.uqhost]
+variable. The function is using integer comparison on `range` and the last
+numeric part of the unqualified host name and string comparison of `prefix`
+(lowercase) with the part of the unqualified host name until the last numeric
+part.
 
 [%CFEngine_function_attributes(prefix, range)%]