code: protected RuntimeConfig buildConfiguration(ServletContext servletContext,
                                                 ExternalContext externalContext, ExpressionFactory expressionFactory)
      {
          RuntimeConfig runtimeConfig = RuntimeConfig.getCurrentInstance(externalContext);
          runtimeConfig.setExpressionFactory(expressionFactory);
  
          // And configure everything
          new FacesConfigurator(externalContext).configure();
  
          validateFacesConfig(servletContext, externalContext);
  
          return runtimeConfig;
      }
docs: Configures this JSF application. It's required that every
  FacesInitializer (i.e. every subclass) calls this method during
  initialization.
  
  @param servletContext    the current ServletContext
  @param externalContext   the current ExternalContext
  @param expressionFactory the ExpressionFactory to use
  @return the current runtime configuration