> > ........ Certainly zero-length intervals are allowed.

>

> Yes. Such intervals would be empty if the end point is

> not considered part of the interval (which

> it normally is, according to a NOTE in [2.1.3].)

I'm still not sure we're on the same page linguistically here.

I'm not even sure what I said was clear.

How about:

"An interval may be a representation of a duration of zero units of

time."

Such as "2006-09-01T00:00:00/2006-09-01T00:00:00"

ISO 8601 allows the second part of the value to be shortened by

omitting the "higher order components" it has in common with the

first part.

So "2006-09-01T00:00:00/2006-09-01T12:00:00"

Can be "2006-09-01T00:00:00/T12:00:00"

(And of course the trailing <:00>s can be removed from both parts.)

It's shortest form (remember I don't like "basic format") would

be: "2006-09-01/T12"

<aside>Which gets into the whole "but you're mixing basic and

extended format" argument.</aside>

So the shortest form of that first (zero-duration) value could

logically be: "2006-09-01/"

This is what I understood you to be asking about -- the second part

is "empty". I answered that this is not compliant (or attempted to

anyway), but I'm going to <em>change my answer!</em> I see nothing

in :2004 section 4.4.5 (:2000 5.5.5) that limits how many of

the "higher-order components" may be omitted or that at least one

component must be present, only that it not be complete, which it

obviously isn't.