What is the problem you're trying to solve?

I think it would be better if this rule supports the ability to check CSS custom properties. For example we have color palette from designers with long complex naming. In this case, it is easy to make the mistake.

:root {
  --companyBrandPaleRed: red;
  --companyBrandP

Describe the bug
Keyframes names like those h1{ -webkit-animation: e836684w2 } h2{ animation: e836684w2 } with e at beginnig are trying to convert by postcss-convert-values

To Reproduce
Here is PR with failing test on this case
cssnano/cssnano#908

Expected behavior
Expected that no conversion performed

Screenshots

**Desktop (please comp

Would be great if you could create a custom plugin for stylelint that adds support for your custom rules; for example, making font-range a known property for the property-no-unknown rule.