Ambiguity with IDN

[jam01]

Through implementing a new validator I ran into some ambiguities with regards to IDN.

The first one I believe is actually a clear issue between the Spec and the Test Suite. The second is more of a question for those more familiar with IDN, though the relevant RFC is where the ambiguity comes from imo.

In both cases the Spec ought to clarify the expected behavior.

idn-hostname:

As defined by either RFC 1123 as for hostname, or an internationalized hostname as defined by RFC 5890

From optional/format/idn-hostname.

{
  "description": "invalid Punycode",
  "comment": "https://tools.ietf.org/html/rfc5891#section-4.4 https://tools.ietf.org/html/rfc5890#section-2.3.2.1",
  "data": "xn--X",
  "valid": false
},

This is a valid RFC 1123, meaning it should pass validation.

idn-email:

As defined by the extended "Mailbox" ABNF rule in RFC 6531

Same test adapted for idn-email format use case.

{
    "description": "invalid Punycode",
    "comment": "https://tools.ietf.org/html/rfc5891#section-4.4 https://tools.ietf.org/html/rfc5890#section-2.3.2.1",
    "data": "schema@xn--X",
    "valid": false
}

Should this fail? rfc6531#3.3 states the subdomains can be LDH or U-labels, it does not explicitly state whether R-LDH labels must be valid A-labels.