s/MUST/SHOULD/ + clarify scope & document.

getusermedia.html

@@ -729,16 +729,17 @@ <h4>Life-cycle</h4>
         <a href="#track-enabled">enabled</a> track sourced by a device exposed
         by <a data-link-for="MediaDevices">getUserMedia()</a> becomes either
         <a href="#track-muted">muted</a> or <a href="#track-enabled">disabled</a>,
-        and this brings <em>all</em> tracks connected to the device to be either
-        muted, disabled, or stopped, then the UA MUST relinquish the device
+        and this brings <em>all</em> tracks connected to the device (regardless
+        of browsing context) to be either
+        muted, disabled, or stopped, then the UA SHOULD relinquish the device
         within 3 seconds while allowing time for a reasonably-observant user to
-        become aware of the transition. The UA MUST attempt to reacquire the
+        become aware of the transition. The UA SHOULD attempt to reacquire the
         device as soon as any <code>live</code> track sourced by the device
         becomes both <a href="#track-muted">unmuted</a> and
-        <a href="#track-enabled">enabled</a> again, provided the <var>document</var>
+        <a href="#track-enabled">enabled</a> again, provided that track's
+        <a>current settings object</a>'s <a>responsible document</a>
         <a data-cite="!HTML/#gains-focus">has focus</a> at that time. If the
-        <var>document</var> does not
-        <a data-cite="!HTML/#gains-focus">have focus</a> at that time,
+        document does not <a data-cite="!HTML/#gains-focus">have focus</a> at that time,
         the UA SHOULD instead queue a task to <a href="#track-muted">mute</a> the
         track, and not queue a task to <a href="#track-muted">unmute</a> it until
         the document <a data-cite="!HTML/#gains-focus">regains focus</a>.