[whatwg/url] Explain why valid domain needs to run ToUnicode (Issue #817)

### What is the issue with the URL Standard?

https://url.spec.whatwg.org/#valid-domain could use an informative note that states the implications of the two-step (both ToASCII and ToUnicode) check. Given the how both use UTS 46 "Processing" and "ToASCII" does more stuff after "Processing", it would be helpful to call out what the second run of "Processing" (as part of "ToUnicode") catches still.

-- 
Reply to this email directly or view it on GitHub:
https://github.com/whatwg/url/issues/817
You are receiving this because you are subscribed to this thread.

Message ID: <whatwg/url/issues/817@github.com>