--- a/ttml10-sdp-us/Overview.html	Thu Sep 20 17:17:45 2012 +0800
+++ b/ttml10-sdp-us/Overview.html	Thu Sep 20 17:19:42 2012 +0800
@@ -1337,7 +1337,7 @@
 <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.</p>
+<p data-transform='constraint'>Durations (dur) SHALL only be used on the span element for rollup style content.</p>
 <p>Note: The use of dur on a span supports rollup style content. For content other than rollup, the default behavior is to remain present until the end of the container. Therefore, durations are not needed on the span element.</p>
 <p data-transform='constraint'>For timing in hh:mm:ss.ms, the following format MUST be used:</p>
 <ul>