--- a/model/optional.html	Mon Apr 02 15:55:11 2012 +0100
+++ b/model/optional.html	Mon Apr 02 15:56:29 2012 +0100
@@ -2,6 +2,8 @@
    <section id="optional"> 
 <h3>Optional Attributes</h3>
 
+PROV-DM allows for some attributes to be optionally expressed. Unless otherwise specified, when an optional attribute is not present in a description, some value SHOULD be assumed to exist for this attribute, though it is not known which.  See <a href="http://dvcs.w3.org/hg/prov/raw-file/default/model/prov-dm-constraints.html#optional-attributes1"> TEXT HERE</a>)
+
 <h4>Time related attributes</h4>
 
 Existence of time implied, if unspecified, since events are instantaneous.