Subject: UTS46 testing for empty labels
Source: Mark Davis
Date: 2014-08-30

(Note: This revision fixes the links to UTS #46 draft, only.)

Erik pointed out that it would be useful in the statement of http://www.unicode.org/reports/tr46/tr46-12.html#ToUnicode to have a check for empty labels (which could result from the string "xn--" or an original ""). That is, the following should be flagged as errors.


but not, of course, with a trailing dot, as in:


Markus and I looked at this, and think that a possible way to do this is to add to http://www.unicode.org/reports/tr46/tr46-12.html#Validity_Criteria

0. The label must have length ≠ 0, if it is not the final label.

There are other ways to do it, also, so feedback would be useful.

Note that in the current version, non-zero length is only checked in http://www.unicode.org/reports/tr46/tr46-12.html#ToASCII, and only if the flag VerifyDnsLength flag is true.