[tei-council] dating attrs

[Syd Bauman]

BTW, the development version of the Guidelines (the one which is in
https://tei.svn.sourceforge.net/svnroot/tei/trunk/P5/Source/ and
available as HTML at
http://bauman.zapto.org/~syd/temp/Guidelines-web/en/html/index.html)
also has all the new dating attributes in it. Since we all voted on
it, I don't think there is much controversial there, except as listed
below. On the other hand, paying close attention for class errors,
typos, etc., would be helpful.

Possible Issues
-------- ------

* Rather than create a new module for ISO dating attributes, I stuck
  'em directly into the namesdates module.

* We never decided on the names of the ISO attributes. I called them
    value-iso=
    dur-iso=
    notBefore-iso=
  etc. My thinking (what little there was) was that it would be nice
  if these attributes sorted near their "simple" W3C counterparts.

* We should perhaps discuss how strong the warnings against using
  "24:00" and basic formats (i.e., no colons or hyphens in some
  cases) should be. Currently the remarks say

    <p>For all representations for which ISO 8601 describes both a
    <term>basic</term> and an <term>extended</term> format, these
    Guidelines recommend use of the extended format.</p>
    <p>While ISO 8601 permits the use of both <code>00:00</code> and
    <code>24:00</code> to represent midnight, these Guidelines
    strongly recommend against the use of <code>24:00</code>. <!-- As
    there are only 24 hours in a day, numbered "00" through "23", use
    of "24:00" implies a 25th hour, and some software may be confused.
    Note that when there is a leap second, it should be indicated
    with 23:59:60. --></p>