Talk about multiple WWW-Authenticate values

Fixes #136

draft-ietf-httpbis-semantics-latest.xml

@@ -10654,6 +10654,11 @@ Content-Encoding: gzip
   "title", and another one for the "Basic" scheme with a realm value of
   "simple".
 </t>
+<t>
+  Some user agents do not recognise this form, however. As a result, sending
+  a WWW-Authenticate field value with more than one member on the same field
+  line might not be interoperable.
+</t>
 <aside>
   <t>
     &Note; The challenge grammar production uses the list syntax as
@@ -13389,6 +13394,7 @@ transfer-coding = &lt;transfer-coding, see <xref target="Messaging" x:fmt="," x:
   <li>In <xref target="field.expect"/>, change the ABNF back to be a list of expectations, as defined in RFC 2616 (<eref target="https://github.com/httpwg/http-core/issues/203"/>)</li>
   <li>Moved definitions of "TE" and "Upgrade" from <xref target="Messaging"/> (<eref target="https://github.com/httpwg/http-core/issues/392"/>)</li>
   <li>Moved definition of "Connection" from <xref target="Messaging"/> (<eref target="https://github.com/httpwg/http-core/issues/407"/>)</li>
+  <li>Noted that "WWW-Authenticate" with more than one value on a line is sometimes not interoperable <xref target="Messaging"/> (<eref target="https://github.com/httpwg/http-core/issues/136"/>)</li>
 </ul>
 </section>
 </section>