"Additional CSS" validate syntax error in customizer

[rishishah]

Validation for Additional CSS in customize is not correct.

STEP TO REPRODUCE

1. Go to "Appearance>Customize"
2. Select "Additional CSS"
3. When I wrote curly brace "{" or "}" inside comment section /* ... */ and save it, it shows me error that

Your curly brackets {} are imbalanced. Make sure there is a closing } for every opening {.

This error should not consider inside comment section /* ... */

[dd32]

See also #39198 for where we removed the check for single quotes ' but left it in place for {, }, and ".

We've also got #39218 to use a tokeniser rather than naive regular expressions.

I don't think we should change it further for the 4.7.x branch myself (unless we backport tokenisation). I'd suggest marking this as a duplicate of #39218.

[westonruter]

Duplicate of #39218.

Agreed. Also, I think that the current server-side validation can be eliminated in favor of client-side validation that will come with a proper code editor component in #38707.