on of <code>ELResolver</code>s, which are used to resolve variables in EL expressions contained
 in JSP pages and tag files.</li>
 <li>Provides an instance of <code>ExpressionFactory</code> for those applications or frameworks that need to perform
 programmatic evaluation of EL expressions instead of allowing the JSP container to do it for them.</li>
 <li>Allows the attachment of <code>ELContextListener</code> instances for notification whenever a new
 <code>ELContext</code> is created. This is necessary wh