Update output role=alert

Author: snuggs

styles/index.html

@@ -2947,6 +2947,10 @@ <h2>Forms</h2>
         <output role=alert for=output-input aria-live=polite>Polite alert text</output>
 
         <header>With <var>role=alert</var><var>aria-live=assertive</var></header>
+        <!-- https://w3c.github.io/aria#alert -->
+        <!-- https://w3c.github.io/aria#aria-live -->
+        <output role=alert for=output-input aria-live=assertive>Assertive alert text</output>
+
 
         <header>With <var>role=note</var></header>
         <!-- https://w3c.github.io/aria//#note -->