--- a/ttml10/spec/ttaf1-dfxp.xml	Wed Jun 19 16:39:39 2013 +0800
+++ b/ttml10/spec/ttaf1-dfxp.xml	Wed Jun 19 17:20:25 2013 +0800
@@ -1935,8 +1935,12 @@
 absolute URI.  In either case (original absolute URI or resulting
 absolutized URI), the URI expressed by the <el>ttp:feature</el>
 element must further adhere to the syntax of a feature designation as
-defined by <specref ref="feature-designations"/>.</p> <p>If
-the URI expressed by the content of the <el>ttp:feature</el> element
+defined by <specref ref="feature-designations"/>, and, furthermore,
+the specific designation that appears in this URI, i.e., the portion of the feature designation
+that starts with the fragment identifier separator '#', must
+be defined by this specification or some published version thereof (that
+has achieved REC status).</p>
+<p>If the URI expressed by the content of the <el>ttp:feature</el> element
 is a relative URI, then an <att>xml:base</att> attribute should be
 specified on the nearest ancestor <el>ttp:features</el> element.</p>
 <p>The <att>value</att> attribute specifies whether a conforming TTML
@@ -1951,7 +1955,6 @@
 <code>use</code>, then the processor must both (1) implement or
 otherwise support the feature and (2) have enabled (activated) use of the
 feature.</p>
-
 <note role="clarification">
 <p>The default value of the <att>value</att> attribute is
 <code>required</code>, as indicated in the above element information

--- a/ttml10/spec/ttml-changes.html	Wed Jun 19 16:39:39 2013 +0800
+++ b/ttml10/spec/ttml-changes.html	Wed Jun 19 17:20:25 2013 +0800
@@ -61,6 +61,9 @@
   element.
 * In 5.2, add note clarifying that the absence of a ttp:profile attribute or ttp:profile
   element is permitted in a conforming document.
+* In 6.1.3, clarify that absolutized feature designation URI must specify a designation
+  (starting with fragment identifier separator) that appears in a published version of
+  the TTML specification (that has reached REC status).
 * In 6.1.3, clarify that the meaning of supporting a required feature is independent of
   whether the feature is enabled (active) or disabled (inactive).
 * In 6.1.3, clarify that when a value of <code>use</code> is specified and the feature