[cabfpub] Ballot 202 - Underscore and Wildcard Characters

[Jacob Hoffman-Andrews]

If people are curious, as I was, about why RFC 5890 restricts use of
Reserved LDH Labels, here is what I believe to be the relevant paragraph:

https://tools.ietf.org/html/rfc5890#page-8

> Labels within the class of R-LDH labels that are not prefixed with
> "xn--" are also not valid IDNA labels.  To allow for future use of
> mechanisms similar to IDNA, *those labels MUST NOT be processed as*

*> ordinary LDH labels by IDNA-conforming programs* and SHOULD NOT be
> mixed with IDNA labels in the same zone.


(emphasis mine)
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