Standardizing on IDNA 2003 in the URL Standard

Gervase Markham gerv at
Thu Aug 22 15:05:34 CEST 2013

On 22/08/13 13:36, Anne van Kesteren wrote:
> As far as UseSTD3ASCIIRules is concerned, I haven't checked if TR46 is
> safe when it comes to
> if you turn that
> flag off.

AIUI, assuming we write our replacement for the STD3ASCIIRules to
disallow "/" in hostnames, we should be fine. When UseSTD3ASCIIRules is
false, "℁" (U+2101) will map to "a/s", and then the "/" will be disallowed.

TR46 section 4.1:

"If UseSTD3ASCIIRules=false, then the validity tests for ASCII
characters are not provided by the table status values, but are
implementation-dependent. For example, if an implementation allows the
characters [\u002Da-zA-Z0-9] and also the underbar (_), then it needs to
use the table values for UseSTD3ASCIIRules=false, and test for any other
ASCII characters as part of its validity criteria. *These ASCII
characters may have resulted from a mapping*: for example, a U+005F ( _
) LOW LINE (underbar) may have originally been a U+FF3F ( _ ) FULLWIDTH

(Emphasis mine.)


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