It's not an error itself but it's detected as it on core-js: https://github.com/zloirock/core-js/blob/master/packages/core-js/internals/regexp-unsupported-ncg.js
It's not an error itself but it's detected as it on core-js: https://github.com/zloirock/core-js/blob/master/packages/core-js/internals/regexp-unsupported-ncg.js