--- a/model/optional.html	Fri Mar 30 15:51:59 2012 +0100
+++ b/model/optional.html	Fri Mar 30 16:01:22 2012 +0100
@@ -4,7 +4,7 @@
 
 <h4>Time related attributes</h4>
 
-
+Existence of time implied, if unspecified, since events are instantaneous.
 <ol>
 <li><a class='attribute' href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#activity.startTime">startTime</a>
 <li><a class='attribute' href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#activity.endTime">endTime</a>
@@ -20,11 +20,11 @@
 <li><a class='attribute' href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#start.trigger">trigger</a> (existence of trigger implied, if not specified)
 <li><a class='attribute' href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#end.trigger">trigger</a> (existence of trigger implied, if not specified)
 <li><a class='attribute' href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#association.agent">agent</a> (existence of agent implied, if not specified)
-<li><a class='attribute' href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#association.plan">plan</a>
+<li><a class='attribute' href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#association.plan">plan</a> (<b>no plan implied</b>, if unspecified)
 <li><a class='attribute' href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#responsibility.activity">activity</a> (existence of activity implied, if not specified)
-<li><a class='attribute' href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#revision.responsibility">responsibility</a>
-<li><a class='attribute' href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#quotation.quoterAgent">quoterAgent</a>
-<li><a class='attribute' href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#quotation.originalAgent">originalAgent</a>
+<li><a class='attribute' href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#revision.responsibility">responsibility</a> (<b>no agent implied</b>, if unspecified)
+<li><a class='attribute' href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#quotation.quoterAgent">quoterAgent</a> (<b>no agent implied</b>, if unspecified)
+<li><a class='attribute' href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm.html#quotation.originalAgent">originalAgent</a> (<b>no agent implied</b>, if unspecified)
 </ol>
 
 <h4>Optional derivation-related</h4>