public static function setViewContext($context = null)
    {
        if ($context === null) {
            $context = self::get(self::get('app.views.context_param', 'format'), 
                                self::get('app.views.default_context', 'html'), 
                                self::get('request'));
        }
        
        self::set('app.view_context', $context);
        
        if (($viewContextParams = self::get("app.views.contexts.$context", false)) !== false) {
            if ($viewContextParams['layout'] !== true) {
                self::set('app.layout', $viewContextParams['layout']);
            }
            header('Content-type: ' . 
                self::get('content_type', 'text/html', $viewContextParams));
        }
    }