From: Syd Bauman
> Sent: Sunday, February 13, 2011 4:15 PM
> Subject: Re: [DATETIME] square bracket

> [1] Like using "--" as an alternate interval separator, which on the
>     face of it seems just plain foolish.

Earlier in the discussion (a few months ago) there was objection raised to,
and apparent popular sentiment against, usage of the slash character for an
interval.  But it really isn't appropriate to profile out the slash in favor
of another syntax because slash is what is used by ISO 8601. As a
compromise, the alternative "--" is allowed as an alternative, so both forms
may be used. Everyone seemed happy with this compromise at the time.

I agree that this leaves the spec vulnerable to criticism but the strong
sentiment against the slash seems to leave no alternative.