RE: [Css Variables] Variable Declaration Blocks

Mike Wilson wrote:
> fantasai wrote:
> > This was as far as I got Friday afternoon at the F2F:
> >    http://fantasai.inkedblade.net/style/specs/constants/
> > It's not very complete, but I think it captures the important points
> > in the discussion.
> 
> The discussion in the meeting notes 
> http://lists.w3.org/Archives/Public/www-style/2008Sep/0075.html
> was kind of brief regarding some of the technical problems with the
> original CSS Vars suggestion.
> <snip>
> So, could you or anyone else elaborate a little on the main technical
> problems?

Hi David (Baron),

I was reading the meeting notes again 
http://lists.w3.org/Archives/Public/www-style/2008Sep/0075.html
and it seems this part was central to changing into the parse-
time route:

  David: The current CSSOM only supports one value per property
         per declaration
  David: You can't do that and get the cascading order right
  David: And change the variables after the fact
  Daniel: Then these need to be constants

The notes are a bit brief so I don't follow this all the way. 
It would be great if you could expand a little on why having 
changeable variables breaks the cascading order?

Best regards
Mike Wilson