--- a/ttml10-sdp-us/Overview.html	Sat Sep 22 14:19:21 2012 +0800
+++ b/ttml10-sdp-us/Overview.html	Mon Sep 24 11:06:16 2012 +0800
@@ -1351,7 +1351,8 @@
 <p>Processors MUST support the capability to present documents where the following constraints apply:</p>
 <p data-transform='constraint'>Timing MUST be expressed in the hh:mm:ss.ms or hh:mm:ss:ff format used in the timeExpression.</p>
 <p data-transform='constraint'>Timing MUST be expressed in the same format throughout the document.</p>
-<p data-transform='constraint'>Durations (dur) SHALL only be used on the span element for Roll-up style content.</p>
+<p data-transform='constraint'>Processors MUST support durations (dur) on the p and span elements, and MAY (but need not) support on other element types;
+as such, a document SHOULD NOT use a duration on an element type other than p or span.</p>
 <p data-transform='constraint'>For timing in hh:mm:ss.ms, the following format MUST be used:</p>
 <ul>
 <li>Exactly 2 digits MUST be used in each of the hours, minutes, and second components (include leading zeros).</li>