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Re: [idn] Tilde

tedd <tedd@sperling.com> wrote:

> Please tell me why mapping the tilde to the tilde operator wouldn't
> work.

It wouldn't be backward compatible.  A primary design goal of IDNA was
that it should not alter the way ASCII domain names are treated.  When
an ASCII domain name contains a tilde, existing software might reject
the name because it expects a host name and RFC-1123 prohibits tilde in
host names, or it might pass the tilde straight through, either because
it is not taking responsibility for enforcing RFC-1123 or because it is
expecting a non-host-name domain name that permits tilde (DNS allows
all ASCII characters).  But in any case, existing software does not map
tilde to something else.

IDNA supports both behaviors.  When UseSTD3ASCIIRules is set, it
prohibits non-LDH ASCII characters, and when UseSTD3ASCIIRules is unset,
it permits all ASCII characters.

AMC

P.S.  For examples of non-host-name domain names, see RFC-2782
(SRV records) and RFC-2317 (PTR records for classless in-addr.arpa
delegation).