[idn] comments on IDNA-04

["James Seng/Personal" <jseng@pobox.org.sg>]

The ToASCII operation takes a sequence of Unicode code points and
transforms it into a sequence of code points in the ASCII range (0..7F).
The original sequence and the resulting sequence are equivalent host
labels.

The ToUnicode operation takes a sequence of Unicode code points and
returns a sequence of Unicode code points. If the input sequence is a
host label in ACE form, then the result is an equivalent host label
that is not in ACE form, otherwise the original sequence is returned
unaltered.

JS>> Suggest to define ASCII Compatible Encoding (ACE) before using it.
then s/ToASCII/ToACE/.

ToACE operation takes a sequence of Unicode code points and transform it
into an ACE.

ToUnicode operation takes an ACE and return a sequence of Unicode code
points.

---
ToASCII consists of the following steps:

    1. If all code points in the sequence are in the ASCII range (0..7F)
       then skip to step 3.


JS>> Step 1 seem to be optimization, but not a required step.

---
The ACE prefix, used in the conversion operations (section 4), will
be specified in a future revision of this document. It will be two
alphanumeric ASCII characters followed by two hyphen-minuses. It MUST
be recognized in a case-insensitive manner.

JS>> Suggest s/ACE prefix/ACE tag/. An "ACE tag" could be a uniquely
defined prefix and/or suffix defined by IANA and not neccessary in the
form of xx--.