[css-counter-styles] dynamic setting of descriptors that would invalidate @counter-style rules

http://dev.w3.org/csswg/css-counter-styles/#the-csscounterstylerule-interface
says:
  #  2. If the returned value is invalid according to the given
  #     descriptor’s grammar, do nothing and abort these steps. 

I think this needs an additional "or would cause the @counter-style
rule to be invalid" to handle cases like the rule in
http://dev.w3.org/csswg/css-counter-styles/#counter-style-symbols
that some 'symbols' descriptors must have two entries, or the rule
in http://dev.w3.org/csswg/css-counter-styles/#override-system that
an @counter-style rule with the 'override' system must not contain a
'symbols' or 'additive-symbols' descriptor.

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                          https://www.mozilla.org/   𝄂
             Before I built a wall I'd ask to know
             What I was walling in or walling out,
             And to whom I was like to give offense.
               - Robert Frost, Mending Wall (1914)