Merge pull request #535 from w3c/randomMid1

update MID to be random values when not received in offer

webrtc.html

@@ -2400,17 +2400,17 @@ <h4>RTCIceCandidate Interface</h4>
           takes a dictionary argument, <var>candidateInitDict</var>, whose content is used
           to initialize the new
           <a class="idlType" href="#idl-def-RTCIceCandidate"><code>RTCIceCandidate</code></a>
-          object. If either <var>sdpMid</var> or <var>sdpMLineIndex</var> is not present in
+          object. If the <var>sdpMLineIndex</var> is not present in
           <var>candidateInitDict</var>, the corresponding attribute will be initialized to
-          <code>null</code>. If neither is present, a <code>TypeError</code> exception
+          <code>null</code>. If <var>sdpMid</var> is not present, a <code>TypeError</code> exception
           will be thrown.</dd>
 
           <dt>readonly attribute DOMString candidate</dt>
 
           <dd>This carries the <code>candidate-attribute</code> as defined in
           section 15.1 of [[!ICE]].</dd>
 
-          <dt>readonly attribute DOMString? sdpMid</dt>
+          <dt>readonly attribute DOMString sdpMid</dt>
 
           <dd>If not <code>null</code>, this contains the identifier of the "media stream
           identification" as defined in [[!RFC5888]] for the media component this
@@ -4136,13 +4136,20 @@ <h3>RTCRtpTransceiver Interface</h3>
           <dt>readonly attribute DOMString? mid</dt>
 
           <dd>
-            <p>The <dfn id=
-            "dom-rtptransceiver-mid"><code>mid</code></dfn>
+            <p>The <dfn id="dom-rtptransceiver-mid"><code>mid</code></dfn>
             attribute is the <code>mid</code> negotatiated and present
             in the local and remote descriptions as defined in
-            <span data-jsep="initial-offers initial-answers">[[!JSEP]]</span>.  Before negotiation is complete,
-            the <code>mid</code> value may be null.  After rollbacks,
-            the value may change from a non-null value to null.</p>
+            <span>[[!JSEP]]</span>.
+            <!--
+            TODO add data-jsep="initial-offers initial-answers" to the span
+            -->
+            Before negotiation is complete, the <code>mid</code> value may be
+            null.  If there is no MID value in the the remote SDP, and no MID
+            value was previously assigned, a random value will be created for
+            the <code>mid</code> as described in <span
+            data-jsep="ice-candidate-format">[[!JSEP]]</span> when the remote
+            SDP is set. After rollbacks, the value may change from a non-null
+            value to null.</p>
           </dd>
 
           <dt>[SameObject] readonly attribute RTCRtpSender sender</dt>