CONTEXTO Proposal

(This dates from July 20, 2009, when the CONTEXTO issue was still open. It is now moot.)


I believe that none of the current CONTEXTO characters are really required to be CONTEXTO, and all should be simply PVALID.

Here are my recommendations in detail:

A. HYPHEN

The rule on HYPHEN is unnecessary, since it is a requirement of the DNS system anyway; this is completely redundant. So remove from Tables:
  • http://tools.ietf.org/html/draft-ietf-idnabis-tables#appendix-A.1

    Appendix A.1. HYPHEN-MINUS

    Code point:
    U+002D
    Overview:
    Must not appear at the beginning or end of a label.
    Lookup:
    False
    Rule Set:
    True;
    If FirstChar .eq. cp Then False;
    If LastChar .eq. cp Then False;

Note that in Protocol we have:

4.2.3.1. Consecutive Hyphens
The Unicode string MUST NOT contain "--" (two consecutive hyphens) in
the third and fourth character positions.

The corresponding Lookup restriction is missing from Protocol and should be added.

B. ARABIC-INDIC DIGITS

The rule on these overlaps with Bidi, and would be simpler and more appropriately moved there, since these are all only of concern with Bidi processing. So remove:
  • http://tools.ietf.org/html/draft-ietf-idnabis-tables#appendix-A.13
  • http://tools.ietf.org/html/draft-ietf-idnabis-tables#appendix-A.14
And change BIDI from:

5. If an EN is present, no AN may be present, and vice versa.

To:

5. If an EN is present, no AN or EXTENDED ARABIC-INDIC digit (U+0660..U+0669) may be present. If an AN is present, no EXTENDED ARABIC-INDIC digit (U+0660..U+0669) may be present.

C. Other CONTEXTO

Remove the other CONTEXTO cases. These consist of only the following 6 characters, and there is no particular problem with making them all simply PVALID in the Exceptions table.

Code
  Name
Motivation?
My Comments
U+00B7  ·  MIDDLE DOT a·b.us vs
a.b.us
but different placement
U+0375  ͵  GREEK LOWER NUMERAL SIGN a͵b.us vs
a,b.us
but , is illegal anyway
U+05F3  ‎׳‎  HEBREW PUNCTUATION GERESH a‎׳‎b.us vs
a'b.us
but ' is illegal anyway
U+05F4  ‎״‎  HEBREW PUNCTUATION GERSHAYIM a״b.us vs
a"b.us
but " is illegal anyway
U+30FB  ・  KATAKANA MIDDLE DOT a・b.us vs
a.b.us
but different placement, width
U+0483  ҃  COMBINING CYRILLIC TITLO a҃b .us unclear motivation; but no worse than other combining marks. If there is any problem with that, just make it DISALLOWED in the Exception section; it is archaic anyway.

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