Specify behaviors of addTransceiver, addTrack, and removeTrack.

webrtc.html

@@ -2478,12 +2478,25 @@ <h3>RTCPeerConnection Interface Extensions</h3>
                 <var>connection</var>'s <a href="#senders-set">set of senders</a>,
                 throw an <code>InvalidParameter</code> exception and abort these
                 steps.</p>
+	      </li>
+
+              <li>
+                <p>If an <code>RTCRtpSender</code> exits in <var>connection</var>'s set of
+                senders that was created by a call to <code>setRemoteDescription</code>
+                with a remote offer and has always had a <code>.track</code>
+                of <code>null</code>, then set that sender's <code>.track</code>
+                to <var>track</var> and return the sender.</p>
+
+		<p>Doing so will cause future calls to <code>createAnswer</code> to mark
+		the m-line for the corresponding transceiver as <code>sendrecv</code>
+		or <code>sendonly</code>, as defined in [[!RTCWEB-JSEP]].
               </li>
 
               <li>
-                <p>Create a new <code>RTCRtpSender</code> for <var>track</var>, add it to
-                 <var>connection</var>'s <a href="#senders-set">set of senders</a>,
-                 and return it to the caller.</p>
+                <p>If no such sender exists, create a new <code>RTCRtpTransceiver</code>
+                with <code>.sender.track</code> set to <var>track</var>, add it to
+                 <var>connection</var>'s set of transceivers, and
+                 return <code>.sender</code> to the caller.</p>
               </li>
 
               <li>
@@ -2516,8 +2529,11 @@ <h3>RTCPeerConnection Interface Extensions</h3>
           <dt>void removeTrack (RTCRtpSender sender)</dt>
 
           <dd>
-            <p>Removes <var>sender</var>, and its associated <code>MediaStreamTrack</code>, from the
-            <code><a>RTCPeerConnection</a></code>.</p>
+            <p>Stops sending media from <var>sender</var>.  The RTCRtpSender will still
+            appear in <code>getSenders</code>. Doing so will cause future calls
+            to <code>createOffer</code> to mark the m-line for the corresponding
+            transceiver as <code>recvonly</code> or <code>inactive</code>, as defined in
+            [[!RTCWEB-JSEP]].
 
             <!-- onended -->
             <p>When the other peer stops sending a track in this manner, an
@@ -2533,7 +2549,7 @@ <h3>RTCPeerConnection Interface Extensions</h3>
                 <p>Let <var>connection</var> be the
                 <code><a>RTCPeerConnection</a></code> object on which the
                 <code><a>RTCRtpSender</a></code>, <var>sender</var>, is to be
-                removed.</p>
+                stopped.</p>
               </li>
 
               <li>
@@ -2550,8 +2566,7 @@ <h3>RTCPeerConnection Interface Extensions</h3>
               </li>
 
               <li>
-                <p>Remove <var>sender</var> from <var>connection</var>'s
-                <a href="#senders-set">set of senders</a>.</p>
+                <p>Stop sending media from <var>sender</var>.</p>
               </li>
 
               <li>
@@ -2564,29 +2579,24 @@ <h3>RTCPeerConnection Interface Extensions</h3>
           DOMString) trackOrKind, RTCRtpTransceiverInit init)</dt>
 
           <dd>
-            <p>Create a new <code><a>RTCRtpTransceiver</a></code> and
-            add it to the collection of transceivers that will be
-            returned
+            <p>Create a new <code><a>RTCRtpTransceiver</a></code> and add it to the
+            collection of transceivers that will be returned
             by <code><a href="#dom-peerconnection-getreceivers">getReceivers()</a></code>.</p>
 
-	    <p>Adding a transceiver will cause future calls
-	    to <code>createOffer</code> to add an m-line for the
-	    corresponding transceiver, as defined in [[!RTCWEB-JSEP]].
+	    <p>Adding a transceiver will cause future calls to <code>createOffer</code> to
+	    add an m-line for the corresponding transceiver, as defined in
+	    [[!RTCWEB-JSEP]].
 
-            <p>If a track is passed in, the value of
-            the <code>.sender.track</code> will be set to that track
-            and the MSID and media type generated
+            <p>If a track is passed in, the value of the <code>.sender.track</code> will
+            be set to that track and the MSID and media type generated
             by <code>createOffer</code> will be that of the track.</p>
 
-            <p>If a kind is passed in, the value of
-            the <code>.sender.track</code> will be null and and media
-            type generated by <code>createOffer</code> will be that of
-            the kind.  The MSID generted by <code>createOffer</code>
-            will be selected by the user agent and will not be related
-            to any track.  Future calls
-            to <code>.sender.replaceTrack</code> must have a track of
-            the same kind and will not change the MSID associated with
-            the transceiver.</p>
+            <p>If a kind is passed in, the value of the <code>.sender.track</code> will be
+            null and and media type generated by <code>createOffer</code> will be that of
+            the kind.  The MSID generated by <code>createOffer</code> will be selected by
+            the user agent and will not be related to any track.  Future calls
+            to <code>.sender.replaceTrack</code> must have a track of the same kind and
+            will not change the MSID associated with the transceiver.</p>
           </dd>
 
           <dt>attribute EventHandler ontrack</dt>