Minor tweak to ascending code unit sort.

Made the example clear that the code units are in the UTF-16 character
encoding.

index.html

@@ -2864,7 +2864,7 @@ <h4>Program Internal Sorting</h4>
 &#x1f63a; (U+1F63A)
 </pre>
 
-		<p>In ascending <em>code unit order</em>, the character U+1F63A is encoded as the code unit sequence <code>0xD83D 0xDE3A</code>, so the strings sort like:</p>	
+		<p>In ascending <em>code unit order</em> in the UTF-16 character encoding, the code point U+1F63A is encoded as the code unit sequence <code>0xD83D 0xDE3A</code> (a [=surrogate pair=]), so the strings sort like:</p>	
 <pre>
 &#x1f63a; (0xD83D 0xDE3A)
 &#xff5e; (0xFF5E)