--- a/ttml2/spec/ttml2-changes.html	Tue Sep 23 12:46:20 2014 -0600
+++ b/ttml2/spec/ttml2-changes.html	Tue Sep 23 12:57:41 2014 -0600
@@ -362,6 +362,9 @@
 * In 9.3, insert "Inline Regions" as sub-section 9.3.2, renumbering following
   sub-sections.
 
+* In 10.3, permit metric component to be omitted from offset-time, in which case
+  's' (seconds) is implied.
+
 * In Appendix H, add (non-normative) reference to CSS Writing Modes Level 3.
 
 * In Appendix H, add (non-normative) reference to Japanese Language Requirements

--- a/ttml2/spec/ttml2.xml	Tue Sep 23 12:46:20 2014 -0600
+++ b/ttml2/spec/ttml2.xml	Tue Sep 23 12:57:41 2014 -0600
@@ -10586,7 +10586,7 @@
 clock-time
   : hours ":" minutes ":" seconds ( fraction | ":" frames ( "." sub-frames )? )?
 offset-time
-  : time-count fraction? metric
+  : time-count fraction? metric?
 hours
   : <loc href="#style-value-digit">&lt;digit&gt;</loc> <loc href="#style-value-digit">&lt;digit&gt;</loc>
   | <loc href="#style-value-digit">&lt;digit&gt;</loc> <loc href="#style-value-digit">&lt;digit&gt;</loc> <loc href="#style-value-digit">&lt;digit&gt;</loc>+
@@ -10634,6 +10634,9 @@
 ref="parameter-attribute-subFrameRate"/>.
 It is considered an error if a <emph>sub-frames</emph> term is specified
 when the <code>clock</code> time base applies.</p>
+<p>If a &lt;timeExpression&gt; is expressed in terms of a
+<emph>offset-time</emph> and no <emph>metric</emph> is specified, then it is to be treated as
+if a metric of <code>s</code> (seconds) were specified.</p>
 </div3>
 </div2> <!-- timing-time-value-expressions -->
 <div2 id="timing-time-intervals">
@@ -11974,10 +11977,10 @@
 a <loc href="#timing-value-timeExpression">&lt;timeExpression&gt;</loc>, and, further, is restricted to use a metric of
 <code>s</code> (seconds),
 <code>f</code> (frames),
-<code>t</code> (ticks), or, exceptionally, may elide the metric, in which case <code>s</code> seconds is implied. This
+<code>t</code> (ticks), or may omit the metric, in which case <code>s</code> seconds is implied. This
 begin time is expressed as an offset from the begin time of the <loc href="#terms-root-temporal-extent">root temporal extent</loc>
 of the source TTML document from which this <loc href="#isd-vocabulary-isd"><el>isd:isd</el></loc> element was derived.</p>
-<p>An <att>end</att> attribute must be similarlly specified, where the same constraints (and exceptional use of no metric) apply.
+<p>An <att>end</att> attribute must be similarlly specified, where the same constraints apply.
 This end time is expressed as an offset from the begin time of the <loc href="#terms-root-temporal-extent">root temporal extent</loc>
 of the source TTML document from which this <loc href="#isd-vocabulary-isd"><el>isd:isd</el></loc> element was derived.</p>
 <note role="elaboration">