[Ltru] rfc4646bis-18 "not suitable" prefix usage

Hi -

As a co-chair and technical contributor...

As part of a close reading of -18 draft of RFC 4646bis...

In section 2.2.5 (page 16/17):
   Variant subtag records in the language subtag registry MAY include
   one or more 'Prefix' fields.  The 'Prefix' indicates a sequence of
   subtags that would make a suitable prefix (with other subtags, as
   appropriate) in forming a language tag with the variant.  That is,
   each of the subtags in the prefix SHOULD appear, in order, before the
   variant.  For example, the subtag 'nedis' has a Prefix of "sl",
   making it suitable for forming language tags such as "sl-nedis" and
   "sl-IT-nedis", but not suitable for use in a tag such as "zh-nedis"
   or "it-IT-nedis".

And on page 26
         nedis" and "sl-IT-nedis" are appropriate, while the tag "is-
         nedis" (Icelandic, Nadiza dialect) is not.

And in section 3.1.8 on page 32
   The 'Prefix' field contains an "extended language range" (see:
   [RFC4647]) whose subtags are appropriate to use with this subtag:
   each of the subtags in one of the subtag's Prefix fields SHOULD
   appear before the variant in a valid tag.  For example, the variant
   subtag '1996' has a 'Prefix' field of "de".  This means that tags
   starting with the sequence "de-" are appropriate with this subtag, so
   "de-Latg-1996" and "de-CH-1996" are both acceptable, while the tag
   "fr-1996" is an inappropriate choice.

Three concerns:
  (1) I am somewhat concerned that the language discouraging
      use of variants with preceding subtags other that those
      enumerated in the Prefix fields is somewhat stronger
      than the sense of WG discussions, where the sentiment
      was repeatedly expressed that Prefix values were not
      intended to be *absolutely* limiting, but merely very
      strong advice, as is already reflected by the SHOULD
      language.  (I think the "pinyin" discussion on ietf-languages
      is also instructive here.)

      I think this concern could be addressed in with
      the following replacement text: replace "not suitable
      for use" in 2.2.5 with -> "not meaningful", replace
      "appropriate" with "meaningful" in the cited passage
      on page 26, and in 3.1.8 replace "is an inappropriate
      choice" with "does not make sense."  Or something like that.

  (2) When we reference extended language range from 4647, do we
      really mean to include the ability to say "-*", and, if so,
      what do we mean by it?

  (3) If we discount the possibility of "-*", then the baroque
      formulation "each of the subtags in one of the subtag's
      Prefix fields SHOULD appear before the variant in a valid
      tag" could be reduced to the slightly simpler "a valid tag
      employing the variant SHOULD begin with a sequence
      of subtags from one of the subtag's Prefix fields."

I don't think any of these is a show-stopper, or should delay
hand-off to the IESG.  They could reasonably be handled as
low-priority IETF last call comments, IMO.

Randy

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