In older EL versions (< 3.0), it's not possible to use constants or any other static fields/methods in an EL expression, as it is not really a good practive to create beans with getter/setter for each constants class, we provide an utils tag which allows to import constant fields in a page. The constants can be accessed via the name of the class (default setting) or via a custom name (var attribute).
<div class="card">
<p:importConstants type="org.primefaces.util.Constants" var="PFConstants"/>
<h5 class="mt-0">Library</h5>
<h:outputText value="#{PFConstants.LIBRARY}" />
<h5>DOWNLOAD_COOKIE</h5>
<h:outputText value="#{PFConstants.DOWNLOAD_COOKIE}" />
</div>