Comments on draft-ietf-idnabis-bidi-04

[Andrew Sullivan]

Dear colleagues,

I have read draft-ietf-idnabis-bidi-04.  Here are my comments.

To begin with, I must emphasise that I have no particular expertise in
any bidirectoinal context.  I can read competently only in
Indo-European languages, and an embarrassing subset of them at that.
So there is a limit to how useful my feedback can be.

In §1.2, we have

   While the document proposes completely new text, most reasonable
   labels that were allowed under the old criterion will also be allowed
   under the new criterion, so the operational impact of the rule change
   is limited.

It would be nice here, I suggest, to offer some definition of what
labels fall outside "most reasonable labels".  The description sounds
too much like, "The labels we picked when we wrote this," which is
indubitably not the impression anyone intended.

There are some terms defined in §1.4.  I think it would be way helpful
to a naive reader to be directed to defs at the beginning of this
section first, and then to say "there are specific BIDI-only terms
also defined here".  So I'd move the reference that's at the end of
this section to the beginning.  I don't feel too strongly about
this, however.  (Also, as an aside, it would be helpful if defs
pointed out more explicitly in its §2.3.3 that there are BIDI-only
terms defined in the BIDI document and not in defs.)

The third paragraph now ends with a comma, so it looks like something
was supposed to be added and wasn't.  Or is this just a typo?

I find this peculiar:

   A "Bidi domain name" is a domain name that contains at least one RTL
   label.

If a domain name is RTL.RTL.RTL, it qualifies under this definition,
even though there is no bidirectionality (all labels have the same
directionality).  Explaining why this is still "bidi" would leave me
less confused.

Rule 1 in §2 says, "The first character must be a character with BIDI
property L, R or AL."  I can't tell whether that must is a requirement
or a statement of fact that is entailed by other IDNA rules.  If it's
a requirement, it presumably ought to be a 2119 MUST; even if not, it
seems that we have to know what to do in case the first character
doesn't match this rule.  If it's an entailment, it'd help to make
that plain, which could be done by restating it, "The first character
will be a character with BIDI property L, R, or AL due to [reason
reference]."

In §3, the text 

   One specific requirement was thought to be problematic, but turned
   out to be satisfied by a string that obeys the proposed rules:

   o  The Character Grouping requirement should be satisfied when
      directional controls (LRE, RLE, RLO, LRO, PDF) are used in the
      same paragraph (outside of the labels).  Because these controls
      affect presentation order in non-obvious ways, by affecting the
      "sor" and "eor" properties of the Unicode BIDI algorithm, the
      conditions above require extra testing in order to figure out
      whether or not they influence the display of the domain name.
      Testing found that for the strings allowed under the rule
      presented in this document, directional controls do not influence
      the display of the domain name.

comes after the discussion of things considered and rejected.  This
leaves me confused about whether the text above is in fact a
requirement or not.  If it is a requirement, then I'd move this
segment to the part before the rejected requirements.

The above are all "nice to have" issues; I think they would make the
resulting text easier to understand.  In general, I think the document
is ready to go.  I've sent a couple nits to the editors directly.

Best regards,

A


-- 
Andrew Sullivan
ajs at shinkuro.com
Shinkuro, Inc.