[Toybox] touch -d underspecified.

[Rob Landley]

Posix
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/touch.html
specifies -d as:

  -d  date_time

  Use the specified date_time instead of the current time. The option
  argument shall be a string of the form:

    YYYY-MM-DDThh:mm:SS[.frac][tz]

  or:

    YYYY-MM-DDThh:mm:SS[,frac][tz]

  where:
...
    T is the time designator, and can be replaced by a single <space>.

The problem is, it doesn't say what a "time designator" is. The two
other hits for "designator" in this page are:

  If the T time designator is replaced by a <space> for the -d
  date_time option-argument, the <space> must be quoted to prevent
  the shell from splitting the argument.

and

  The -d date_time format is an ISO 8601:2000 standard complete
  representation of date and time extended format with an optional
  decimal point or <comma> followed by a string of digits following
  the seconds portion to specify fractions of a second. It is not
  necessary to recognize "[+/-]hh:mm" and "[+/-]hh" to specify
  timezones other than local time and UTC. The T time designator in
  the ISO 8601:2000 standard extended format may be replaced by
  <space>.

The touch man page is useless (and points me at the info page, which I'm
not reading).

Googling for "posix time designator" brought up wikipedia pages on unix
time (numeric seconds since 1970), an "epoch coverter" web page where
you type in a time and it converts  it, and then
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwj6rZrzj-DPAhVH2oMKHb94BPQQFggrMAI&url=http%3A%2F%2Fwww.cl.cam.ac.uk%2F~mgk25%2Fiso-time.html&usg=AFQjCNH7F2PiT1zZ22oAVRzQxGByEdcrfA
is the first possibly relevant hit (isn't it FUN how google mangles
links when you right click copy link?) but it does not include the word
"designator". So that's nice.

The _examples_ on the posix page all use "T" for the "designator", so
that's what I made my code do when I wrote it. But somebody complained
(who I promised to stop listening to after they complained about my
'wall of text" instead of just taking the "simple" memcpy->memmove
patch), and although I'm not replying directly to them a bug report's a
bug report...

I checked what busybox is doing, and they're funneling stuff through a
large complicated library function that hardwires in a dozen different
formats checking them in a lage if/else staircase, and among those are
two that accept this format with "-" or " " as "designators". (But not
"T" which is what the posix examples use...)

Does anybody know what this field is supposed to _mean_? And/or have an
actual use case in the wild using touch -d?

Rob