diff --git a/preserves-text.md b/preserves-text.md
index a6e9ca4..d9eb5ad 100644
--- a/preserves-text.md
+++ b/preserves-text.md
@@ -54,7 +54,10 @@ label-`Value` followed by its field-`Value`s.
 curly-brace-enclosed colon-separated pairs of values. `Set`s are
 written as values enclosed by the tokens `#{` and
 `}`.[^printing-collections] It is an error for a set to contain
-duplicate elements or for a dictionary to contain duplicate keys.
+duplicate elements or for a dictionary to contain duplicate keys. When
+printing sets and dictionaries, implementations *SHOULD* order
+elements resp. keys with respect to the [total order over
+`Value`s](preserves.html#total-order).[^rationale-print-ordering]
 
           Sequence = "[" *Value ws "]"
         Dictionary = "{" *(Value ws ":" Value) ws "}"
@@ -68,6 +71,12 @@ duplicate elements or for a dictionary to contain duplicate keys.
     commas separating, and commas terminating elements or key/value
     pairs within a collection.
 
+  [^rationale-print-ordering]: **Rationale.** Consistently printing
+    the elements of unordered collections in some arbitrary but stable
+    order helps, for example, keep diffs small and somewhat meaningful
+    when Preserves values are pretty-printed to text documents under
+    source control.
+
 `Boolean`s are the simple literal strings `#t` and `#f` for true and
 false, respectively.