diff --git a/xep-0016.xml b/xep-0016.xml
index 4ade7b32..a5de7176 100644
--- a/xep-0016.xml
+++ b/xep-0016.xml
@@ -138,7 +138,7 @@
       <li>&lt;domain&gt; (the domain itself matches, as does any user@domain or domain/resource)</li>
     </ol>
     <p>If the type is "group", then the 'value' attribute SHOULD contain the name of a group in the user's roster.  (If a client attempts to update, create, or delete a list item with a group that is not in the user's roster, the server SHOULD return to the client an &lt;item-not-found/&gt; stanza error.)</p>
-    <p>If the type is "subscription", then the 'value' attribute MUST be one of "both", "to", "from", or "none" as defined <cite>RFC 3921</cite>, where "none" includes entities that are totally unknown to the user and therefore not in the user's roster at all.</p>
+    <p>If the type is "subscription", then the 'value' attribute MUST be one of "both", "to", "from", or "none" as defined <cite>RFC 3921</cite>, where "none" includes entities that are totally unknown to the user and therefore not in the user's roster at all. These values are exact matches, so that "both" means a bidirectional subscription (not "from" or "to" only).</p>
     <p>If no 'type' attribute is included, the rule provides the "fall-through" case.</p>
     <p>The 'action' attribute MUST be included and its value MUST be either "allow" or "deny". <note>An implementation MUST NOT block communications from one of a user's resources to another, even if the user happens to define a rule that would otherwise result in that behavior.</note></p>
     <p>The 'order' attribute MUST be included and its value MUST be a non-negative integer that is unique among all items in the list.  (If a client attempts to create or update a list with non-unique order values, the server MUST return to the client a &lt;bad-request/&gt; stanza error.)</p>