Add note about repeated selectors increasing specificity

Author: fantasai

selectors3/Overview.html

@@ -2454,6 +2454,9 @@ <h2><a name=specificity>9. Calculating a selector's specificity</a></h2>
 </pre>
 </div>
 
+<p class="note"><strong>Note:</strong> Repeated occurrances of the
+same simple selector are allowed and do increase specificity.</p>
+
 <p class="note"><strong>Note:</strong> the specificity of the styles
 specified in an HTML <code>style</code> attribute is described in CSS
 2.1. <a href="#refsCSS21">[CSS21]</a>.</p>