Close #91: Mention stand-in items

draft-ietf-core-href.md

@@ -85,6 +85,7 @@ normative:
   STD94: cbor
 # RFC8949
   RFC9165: cddlcontrol
+  I-D.ietf-cbor-packed: packed
 
 --- abstract
 
@@ -468,6 +469,16 @@ references:
   as per {{ingest}} equivalent to `[0]`, which essentially copies the
   base CRI).
 
+Application specifications that use CRIs may explicitly enable the use
+of "stand-in" items (tags or simple values), i.e., items used in place
+of original representation items such as strings or arrays, where the
+tag or simple value is defined to evaluate to the original item that
+it is standing in place of.
+Examples would be tags such as 21 to 23 ({{Section 3.4.5.2 of
+RFC8949@-cbor}}), which might be used to represent text string
+components by employing more compact byte strings, or reference tags and
+simple values as defined in {{-packed}}.
+
 For interchange as separate encoded data items, CRIs MUST NOT use
 indefinite length encoding (see
 {{Section 3.2 of RFC8949@-cbor}}); this requirement is relaxed for