Clarify with notes

webrtc.html

@@ -11340,14 +11340,23 @@ <h2>
                 </p>
                 <p>
                   This method allows applications to disable the negotiation of
-                  specific codecs (including RTX/RED/FEC). It also allows an
-                  application to affect the remote peer's default codecs;
-                  influencing both what they should send by default and the
-                  default codec order of subsequently generated remote SDP. But
-                  just like the local peer can override its defaults, so can the
-                  remote peer. The local peer MUST be prepared to receive any
-                  codec that has been negotiated, even ones not first in the
-                  list.
+                  specific codecs (including RTX/RED/FEC) by listing all codecs
+                  except for the ones to disable.
+                </p>
+                <p class="note">
+                  If the m= section is used for receiving, the order of the
+                  codecs in the SDP (both the offer and the answer) tells the
+                  remote endpoint which codec the local endpoint prefers to
+                  receive. The answerer defaults to using the order in the SDP
+                  offer, but overrides this with their own codec preferences if
+                  they have any.
+                </p>
+                <p class="note">
+                  An RTCRtpSender defaults to sending what the remote endpoint
+                  indicated that it prefers to receive, but the application can
+                  change which codec to send amongst negotiated codecs in
+                  setParameters() at any time. An RTCRtpReceiver is prepared to
+                  receive any negotiated codec.
                 </p>
                 <!-- 'until this method is called again' is not clear. Ditto for 'any default value' -->
                 <p class="needs-test">