[css-transitions-2] Add commonly raised issues deferred from transitions level 1.

Author: dbaron

css-transitions-2/Overview.bs

@@ -45,7 +45,41 @@ Ignored Terms: translate, rotate, scale
 			</ul>
 	</dl>
 
-<h2 id="issues">Issues deferred from previous levels</h2>
+<h2 id="issues-common">Issues commonly raised as issues with previous levels</h2>
+
+	<p>
+		These issues were commonly reported issues
+		with the previous level of the specification.
+	</p>
+
+	<div class="issue">
+		<p>
+			More powerful timing function syntax
+			is a common request from developers.
+			See, for example:
+			<a href="https://lists.w3.org/Archives/Public/www-style/2013Jun/0376.html">2013 message</a>
+			or
+			<a href="https://lists.w3.org/Archives/Public/public-fx/2015JulSep/thread.html#msg34">2015 thread</a>.
+		</p>
+	</div>
+
+	<div class="issue">
+		<p>
+			Developers frequently have to trigger style flushes
+			in order to force transitions to start.
+			It would be good to have an API
+			that would avoid this requirement.
+			See, for example,
+			<a href="https://lists.w3.org/Archives/Public/www-style/2011Mar/0729.html">2011 proposal</a>.
+		</p>
+	</div>
+
+<h2 id="issues-spec">Issues deferred from previous levels of the spec</h2>
+
+	<p>
+		These issues were in previous levels of the specification,
+		but may not turn out to be important in this level either.
+	</p>
 
 	<div class="issue">
 		We may ultimately want to support a keypath syntax