If you try to load a trivial Facelets page, then you get this exception:

javax.faces.FacesException: Problem in renderResponse: Could not instantiate feature[compiler.ExpressionFactory]: com.sun.el.ExpressionFactoryImpl
    com.icesoft.faces.facelets.D2DFaceletViewHandler.renderResponse(D2DFaceletViewHandler.java:324)
    com.icesoft.faces.application.D2DViewHandler.renderView(D2DViewHandler.java:153)
    com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:87)
    com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:200)
    com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:117)
    com.icesoft.faces.webapp.http.core.PageServer$1.respond(PageServer.java:26)
    com.icesoft.faces.webapp.http.servlet.ServletRequestResponse.respondWith(ServletRequestResponse.java:143)
    
*root cause*

com.sun.facelets.FaceletException: Could not instantiate feature[compiler.ExpressionFactory]: com.sun.el.ExpressionFactoryImpl
    com.sun.facelets.compiler.Compiler.featureInstance(Compiler.java:157)
    com.sun.facelets.compiler.Compiler.createExpressionFactory(Compiler.java:146)
    com.sun.facelets.impl.DefaultFaceletFactory.createFacelet(DefaultFaceletFactory.java:193)
    com.sun.facelets.impl.DefaultFaceletFactory.getFacelet(DefaultFaceletFactory.java:141)
    com.sun.facelets.impl.DefaultFaceletFactory.getFacelet(DefaultFaceletFactory.java:93)
    com.icesoft.faces.facelets.D2DFaceletViewHandler.renderResponse(D2DFaceletViewHandler.java:303)
    com.icesoft.faces.application.D2DViewHandler.renderView(D2DViewHandler.java:153)
    com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:87)
    com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:200)
    com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:117)
    com.icesoft.faces.webapp.http.core.PageServer$1.respond(PageServer.java:26)
    com.icesoft.faces.webapp.http.servlet.ServletRequestResponse.respondWith(ServletRequestResponse.java:143)


It appears that, under Tomcat 6, they have their own EL implementation, and don't use the com.sun.el.* one. With Facelets 1.1.11 (not sure about Facelets 1.1.14) there is a "feature" called "compiler.ExpressionFactory" which defaults to "com.sun.el.ExpressionFactoryImpl". Trying to instantiate that class is what causes the exception. There's a method on the Compiler class to set this "feature", but I'm not aware of any code that itself grabs it out of the web.xml.

So, we could add code to set the feature from the web.xml ourself, and then tell people how to configure their web.xml with Tomcat 6 and JSF 1.1 to use this.

Or, we could make a small JAR with a dummy com.sun.el.ExpressionFactoryImpl class that would delegate to the Apache ExpressionFactory, and tell people to just include that JAR with their WAR.

Or, since we ship our own Facelets, we could alter it so that if nothing is configured, it would first try the com.sun.el ExpressionFactory and then try the org.apache ExpressionFactory. That would only take 3 lines of code or so.