This article has a compliance checklist found in the Resources and explains that there are no such things as a Zero Error website.

Zero Errors

There are no error-free sites. It’s a fluid measurement, and different scan tools produce different results. Moreover, there is much that is open to interpretation. The most important thing you can do is to show an ongoing good-faith effort to keep your content compliant. To learn more about what you can do, please view our tools and resources.

Resources