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 "cool" 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).
<p:importConstants type="org.primefaces.util.Constants" var="PFConstants" /> LIBRARY: <h:outputText value="#{PFConstants.LIBRARY}" /> <br /> DOWNLOAD_COOKIE: <h:outputText value="#{PFConstants.DOWNLOAD_COOKIE}" />