[selectors-4] Add some issues.

Author: fantasai

selectors/Overview.bs

@@ -2063,6 +2063,8 @@ The Drag-and-Drop Pseudo-class: '':drop'' and '':drop()''</h3>
 	'':drop()'' has the same meaning as '':drop''
 	- it matches every drop target.
 
+	Issue: Make sure <a href="http://forums.mozillazine.org/viewtopic.php?f=18&t=2633249">this problem</a> is handled.
+
 <h2 id="time-pseudos">
 Time-dimensional Pseudo-classes</h2>
 
@@ -2319,6 +2321,8 @@ The User-interaction Pseudo-class: '':user-error''</h4>
 
 	Issue: Look into :-moz-ui-valid as well.
 
+	Issue: Evaluate proposed <a href="https://lists.w3.org/Archives/Public/www-style/2014Feb/0511.html">:dirty pseudo-class</a>
+
 <h2 id="structural-pseudos">
 Tree-Structural pseudo-classes</h2>