Improve wording based on feedback from @Flowdalic

xep-0033.xml

@@ -286,20 +286,19 @@
 
     <section1 topic='Business Rules' anchor='rules'>
       <section2 topic='Directed Presence' anchor='presence'>
-        <p>To ensure that entities that have received directed
-        presence through a multicast service will get the unvailable
-        presence when the originating client closes the its session,
-        the multicast service should also relay unvailable presence
-        stanzas.</p>
-        <p>When transferring an extended addressing presence stanza,
-        the multicast service MUST keep track of the entities that
-        have received the individual directed presence packets.</p>
-        <p>When the multicast service receive an unavailable presence
-        stanza without extended addresses, it MUST broadcast the
-        updated presence to all the entities that have received a
-        directed presence previously (if the multicast service has not
-        yet sent unavailable presence to a precise entity through a
-        previous extended stanza presence).</p>
+
+        <p>The multicast service MUST keep track of the entities it
+        sent a presence with an absent 'type' attribute (i.e. an
+        'available' presence) to and the originating entity of that
+        presence. If the multicast service receives an unavailable
+        presence from one of the tracked originating entities, it MUST
+        broadcast this presence to all tracked entities which have not
+        yet received an unavailable presence from the originating
+        entity, even if the presence does not contain explicit
+        broadcast addresses. Thus the multicast service ensures that
+        all entities, which have received an (directed) 'available'
+        presence over it, receive the related 'unavailable'
+        presence.</p>
       </section2>
     </section1>