(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:
The rule on HYPHEN is unnecessary, since it is a requirement of the DNS system anyway; this is completely redundant. So remove from Tables:
Appendix A.1. HYPHEN-MINUS
Must not appear at the beginning or end of a label.
If FirstChar .eq. cp Then False;
If LastChar .eq. cp Then False;
Note that in Protocol we have:
188.8.131.52. 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:
And change BIDI from:
5. If an EN is present, no AN may be present, and vice versa.
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.