protected function registerCombinerEvents()
    {
        if (App::runningInBackend() || App::runningInConsole()) {
            return;
        }

        Event::listen('cms.combiner.beforePrepare', function ($combiner, $assets) {
            $filters = array_flatten($combiner->getFilters());
            ThemeData::applyAssetVariablesToCombinerFilters($filters);
        });

        Event::listen('cms.combiner.getCacheKey', function ($combiner, $holder) {
            $holder->key = $holder->key . ThemeData::getCombinerCacheKey();
        });
    }