[css-image] gradient midpoints

All,
I have a couple of question about the current wording of midpoints for CSS
gradients.

1. The spec [1] contains 2 contradictory statements:

Similarly, the color of a color stop can be omitted. The causes the color
to be automatically computed to halfway between the two surrounding stops,
so that the "midpoint" of a transition can be easily adjusted. *If multiple
stops in a row lack a color, they space themselves out equally in "color
space", giving more control over the smoothness of the transition.*

and:

There can only be at most one color interpolation hint between any two
given normal color stops; using more than that makes the function invalid.

I think the second statement is the correct one since exponential
interpolation between midpoints is not defined.

2. The spec also doesn't require that a midpoint is not the first or last
stop in a gradient.

3. I think it's OK to assume that a midpoint that coincides with a regular
stop, does nothing?

4. It is now legal to write a color stop with no information at all.
For instance: linear-gradient(white 0%,,black 100%) -> note the two commas.
Is this OK?

1: http://dev.w3.org/csswg/css-images-4/#color-interpolation-hint