private function extractUsedClasses(&$placeholder)
    {
        $classNamespaceRegExp = '/([\\\\a-zA-Z0-9_]*\\\\[\\\\a-zA-Z0-9_]*)/';
        $matches = [];
        $usedInModelClasses = [];
        if (preg_match_all($classNamespaceRegExp, $placeholder, $matches)) {
            foreach ($matches[1] as $match) {
                $usedClassName = $match;
                $usedInModelClasses[] = trim($usedClassName, '\\');
                $namespaceParts = explode('\\', $usedClassName);
                $resultClassName = array_pop($namespaceParts);
                $placeholder = str_replace($usedClassName, $resultClassName, $placeholder);
            }
        }

        return array_unique($usedInModelClasses);
    }