Piwik\AssetManager\UIAssetMerger::concatenateAssets PHP Method

    protected function concatenateAssets()
    {
        $mergedContent = '';
        foreach ($this->getAssetCatalog()->getAssets() as $uiAsset) {
            $uiAsset->validateFile();
            $content = $this->processFileContent($uiAsset);
            $mergedContent .= $this->getFileSeparator() . $content;
        }
        $this->mergedContent = $mergedContent;
    }