diff --git a/index.html b/index.html
index 048f243..44ee42d 100644
--- a/index.html
+++ b/index.html
@@ -643,12 +643,15 @@ <h2>Security</h2>
           </ul>
         </div>
         <p><span class="rfc2119-assertion" id="common-constraints-security-2">
-            Conformant Consumers MUST support all of these security schemes.</span>
+            Conformant Consumers MUST support at least all of these security schemes.</span>
         </p>
 
         <p><span class="rfc2119-assertion" id="common-constraints-security-3">
             A Thing MAY implement multiple security schemes.</span>
         </p>
+        <p><span class="rfc2119-assertion" id="common-constraints-security-4">
+            A Thing MUST support at least one of the above security schemes.</span>
+        </p>
 
         <p><span class="rfc2119-assertion" id="common-constraints-security-6">
           Conformant Consumers MUST support security bootstrapping for all
@@ -901,7 +904,7 @@ <h3>Media Types for Link Targets</h3>
 
     <!-- Errors -->
     <section id="common-constraints-errors">
-      <h2 id="error-responses">Errors</h2>
+      <h3 id="error-responses">Errors</h3>
       <p>
         <span class="rfc2119-assertion" id="common-constraints-errors-1">
           If any of the operations defined in the protocol bindings of HTTP
@@ -920,6 +923,7 @@ <h2 id="error-responses">Errors</h2>
           <li><code>403 Forbidden</code></li>
           <li><code>404 Not Found</code></li>
           <li><code>500 Internal Server Error</code></li>
+          <li><code>503 Service Unavailable</code></li>
         </ul>
       </div>
       <p>
@@ -956,6 +960,56 @@ <h2>Default Language</h2>
           (e.g., en, de-AT, gsw-CH, zh-Hans, zh-Hant-HK, sl-nedis).</span>
         </span>
     </section>
+    <section id="sec-identifiers">
+      <h2>Identifiers</h2>
+      <p>
+        Web resources are identified by uniform resource identifiers (URIs).
+        The Thing Description defines the field <a href="https://w3c.github.io/wot-thing-description/#thing><code>id</code></a>
+	      for that purpose, which is in the format "anyURI".
+      </p>
+      <p>
+        In deployments of multiple devices in the same application context, things must be distinguished by the consumer.
+        In these cases, these identifiers must be <em>unique</em>.
+        Use cases with worldwide deployments typically require <em>globally</em> unique identifiers.
+      </p> 
+      <section id="sec-identifiers-format">
+        <h3>Format</h3>
+      <p>
+        A common and well defined format for these identifiers enables easy implementation 
+        and simplifies handling across manufacturers through the use of libraries. 
+        It also ensures that there are no name clashes of devices from different manufacturers.
+        The [[UUID]] format has been developed to satisfy these requirements.
+      </p>
+        <p>
+          <span class="rfc2119-assertion" id="common-constraints-identifiers-uuid">
+            It is RECOMMENDED to use Universally Unique IDentifier (UUID) [[RFC4122]] as common format for identifers.
+          </span>
+        </p>
+          <span class="rfc2119-assertion" id="common-constraints-identifiers-random">
+          It is RECOMMENDED to use [[UUIDv4]] as common format for unique identifers, where random identifiers are required.
+          </span>
+      </p>
+      </section>
+      <section id="sec-identifiers-mutability">
+        <h3>Mutable and Immutable Identifiers</h3>
+      <p>
+        Many use cases require that identifiers do not change during the lifecycle of the thing in the application context.
+        However there are cases, where the IDs must change due to legal or privacy obligations. 
+        IDs should be changed when a device is offboarded and onboarded on a new system (e.g. for change
+        of ownership).
+        In these cases, or when a device is moved to a new usage context, identifiers usually must change. 
+      </p>
+
+      <p><span class="rfc2119-assertion" id="common-constraints-identifiers-mutable">
+        In certain use cases where privacy is a factor or legal obligations mandate changing identifiers, 
+        the use of a <em>mutable UUID</em> is RECOMMENDED.</span>
+      </p>
+
+      <p><span class="rfc2119-assertion" id="common-constraints-identifiers-immutable-ids">
+        If possible and allowed by law, required immutable IDs SHOULD be made available through a
+        property rather than used as the id for the TD itself.
+      </span></p>
+      </section>
   </section>
 
 
@@ -1667,7 +1721,18 @@ <h6 id="async-action-response">Asynchronous Action Response</h6>
               "timeRequested": "2021-11-10T11:43:19.135Z"
             }
           </pre>
-        </section>
+          <div class="rfc2119-assertion" id="http-basic-profile-protocol-binding-invokeaction-22">
+          <p>
+            In resource constrained environments, the ActionStatus objects of older completed/failed actions MAY be deleted to make room for newly invoked actions.
+          </p>
+          </div>
+          <div class="rfc2119-assertion" id="http-basic-profile-protocol-binding-invokeaction-23">
+          <p>
+            A Web Thing SHOULD return a <code>503</code> error response if the invocation cannot be accepted because the action is unavailable,
+            e.g. because the Thing is overloaded.
+          </p>
+          </div>
+         </section>
 
         <section id="http-basic-profile-protocol-binding-queryaction">
           <h5><code>queryaction</code></h5>