[css3-flexbox] component properties of flex

We have an issue to resolve for dealing with flex values in DOM: https://www.w3.org/Bugs/Public/show_bug.cgi?id=16145

I think the most reasonable way to do it is to actually have component properties:

                flex-negative
                flex-positive
                flex-preferred-size

or
                flex-grow
                flex-shrink
                flex-base

or something like that.

They will of course be automatically available in DOM, no special-case API needed.

We didn't get component properties upfront because we had flex() function and we have convinced ourselves that it is OK to have to set all three values together and not have them cascade separately. I don't think we have convincing arguments though that they must not cascade separately. These properties will usually together, just like border width and border style typically do, but I can think of plenty of use cases where flexibility components are assigned to categories of items, controlled by pseudo classes or animated separately, without any loss of conceptual integrity and consistent to how CSS works everywhere else.

I propose adding the component properties, as listed above or with even more intuitive naming (and we are very good in naming things!).

Alex