[selectors] Add issue about an+b being defined in Syntax now.

Author: tabatkins

selectors/Overview.html

@@ -3560,6 +3560,10 @@ <h4 id=anb-syntax><span class=secno>12.4.1. </span> Syntax</h4>
 
   <h4 id=anb-grammar><span class=secno>12.4.2. </span> Grammar</h4>
 
+  <p class=issue> A better definition of the grammar now exists in the Syntax
+   spec. Once that spec hits WD, we should remove this section in favor of
+   just pointing to Syntax.
+
   <p> An informative definition of the <a href="#anb0"><var>An+B</var></a>
    syntax is:
 

selectors/Overview.src.html

@@ -2480,6 +2480,11 @@ <h4 id='anb-syntax'>
 <h4 id='anb-grammar'>
 Grammar</h4>
 
+  <p class='issue'>
+    A better definition of the grammar now exists in the Syntax spec.
+    Once that spec hits WD,
+    we should remove this section in favor of just pointing to Syntax.
+
   <p>
     An informative definition of the <var>An+B</var> syntax is: