Merge pull request #477 from UlfBj/issue473

Issue473 agreed on during WG call

spec/VISSv2_Core.html

@@ -440,8 +440,10 @@ <h2>Subscription</h2>
       <section id="error-message">
         <h2>Error Message</h2>
         <p>The server MUST inform a client about errors ocurring in interactions between the two, whether it is in a synchronous 
-        error response, or an asynchronous error event message as a result of a previous subscribe. The error message has three arguments, 
-        of which subscriptionId is mandatory only for error event messages.
+        error response, or an asynchronous error notification as a result of a previous subscribe. 
+        For transport protocols which do not control the logical linking between request and response messages it may not be possible to link an error message to the correct client request. 
+        In cases like this the server may omit sending an error message. 
+        The error message has three arguments, of which subscriptionId is mandatory only for error notifications.
         </p>
           <p>Arguments: 
             <ul>

spec/VISSv2_Transport.html

@@ -1498,8 +1498,7 @@ <h2>Term Definitions</h2>
 	  <tr>
 	    <td> <dfn data-dfn-type="dfn" id="dfn-subscriptionid">subscriptionId</dfn> </td>
             <td>String</td>
-	    <td>Value returned by the server to uniquely identify each subscription.
-	    The value <em class="rfc2119" title="MAY">MAY</em> be an integer or a Universally Unique Identifier (UUID).</td>
+	    <td>Value returned by the server to uniquely identify each subscription.</td>
 	  </tr>
 	  <tr>
 	    <td><dfn data-dfn-type="dfn" id="dfn-authorization">authorization</dfn> </td>