8220;Post/Redirect/Get&#8221; design pattern.
 </p>

 <p>
 The implementation must allow the user to access the flash via the Jakarta Expression Language implicit object
 <code>flash</code> and also via <a href="ExternalContext.html#getFlash()"><code>ExternalContext.getFlash()</code></a>. The implementation must
 ensure that the flash is usable from both Jakarta Server Pages and from Facelets for Jakarta Faces 2. In
 addition to exposing the <code>Map</code> interface, there are several features exposed as 