Recently, I've encouraged some fellows to implement JavaFX VDL ( http://alexsmirnov.wordpress.com/tag/javafx/ ), and we got inconsistent requirements in the spec that makes ViewDeclarationLanguage implementation close depended from ViewHandler implementation. Description of the ViewHandler#writeState says: public void writeState(FacesContext context) throws IOException; Take any appropriate action to either immediately write out the current view’s state information (by calling StateManager.writeState()), or noting where state information may later be written. There are no requirements for viewHandler implementation how to write state late. On the other hand, default implementation should call ViewDeclarationLanguage#renderView method that creates appropriate writer and put actual state. Therefore, it is not possible to introduce custom ViewDeclarationLanguage without ViewHandler modifications. Possible solutions are: 1) Introduce ViewDeclarationLanguage#writeState method that should be called from ViewHandler#writeState in the same way as renderView method does. 2) Change default ViewHandler#renderView method requirements that it should create appropriate ResponseWriter before calling ViewDeclarationLanguage#renderView method, so ViewHandler can perform late state writing in consistent way. I prefer to the #2 solution because that allows to reduce duplicated code in the ViewDeclarationLanguage implementations, but there is a problem: VDL may provide additional options for response like buffer sixe, encoding and content type that required to create ResponseWriter. Possible solution is to make public ViewDeclarationLanguage#createResponseWriter(FacesContext context) method that already exists in the Mojarra implementation.