Merge pull request #2027 from w3c/note-on-duration

epub33/rs/index.html

@@ -1835,7 +1835,9 @@ <h5>Text-to-Speech</h5>
 						associated speech synthesis. The implicit duration of the <code>text</code> element (and by
 						inference, of the parent <code>par</code> element) is therefore determined by the execution of
 						the Text-to-Speech engine, and cannot be known at authoring time (factors like speech rate,
-						pauses and other prosody parameters influence the audio output).</p>
+						pauses and other prosody parameters influence the audio output).
+						This also means that Reading Systems should treat the data-cite="epub-33#duration"><code>duration</code></a> property values set in the Package Document as approximative when making use of them.
+					</p>
 				</section>
 			</section>