diff --git a/scribble-doc/scribblings/scribble/core.scrbl b/scribble-doc/scribblings/scribble/core.scrbl
index f8da400b..8ef8209a 100644
--- a/scribble-doc/scribblings/scribble/core.scrbl
+++ b/scribble-doc/scribblings/scribble/core.scrbl
@@ -1351,7 +1351,7 @@ Returns the width in characters of the given @tech{block}.}
 @defproc[(part-number-item? [v any/c]) boolean]{
 
 Return @racket[#t] if @racket[v] is @racket[#f], an exact non-negative
-integer, a string, or a list containing two strings. See @racket[part]
+integer, a string, or a list containing two strings. See @racket[collected-info]
 for information on how different representations are used for numbering.
 
 @history[#:added "6.4"]}
@@ -1400,6 +1400,15 @@ identity is based on a @racket[generated-tag]. The result of
 number plus an updated hash table with an incremented value for the
 @tech{numberer}.
 
+Typically, the rendered form of a section number (produced by
+@racket[numberer-step]) is a list containing two strings. The first
+string is the part's immediate number, which can be combined with a
+prefix for enclosing parts' numbers. The second string is a separator
+that is placed after the part's number and before a subsection's
+number for each subsection. If @racket[numberer-step] produces a plain
+string for the rendered number, then it is not added as a prefix to
+subsection numbers. See also @racket[collected-info].
+
 @history[#:added "6.4"]}