Request supporting validator.w3.org/nu service #12258

Are you experiencing an issue with...

shields.io

🐞 Description

The old engine is no longer suitable to new website standard. For instance:

• Failed on hgroup tag

I would like to support https://validator.w3.org/nu alongside with https://validator.nu

🔗 Link to the badge

https://shields.io/badges/w-3-c-validation

Sample:

![W3C Validation](https://img.shields.io/w3c-validation/html?targetUrl=https%3A%2F%2Fngdangtu.com)

💡 Possible Solution

Old service should not be removed because new service is easily blocked by cloudflare (not sure why - but you can try it with my domain). Therefore, I suggest to support both service at the same time with 2 new options:

1. serivce with 2 values: old, new; default is old so we don't mess old badges
2. fallback with boolean where true will use the other service if the high priority lost connection; default is false with the same reason above