[css3-fonts] 'font-variant' shorthand missing sub and supert values (for font-variant-position)

The grammar for the 'font-variant' shorthand at:
  http://dev.w3.org/csswg/css-fonts/#propdef-font-variant
appears to be missing the 'sub' and 'super' values for the
'font-variant-position' subproperty defined at
http://dev.w3.org/csswg/css-fonts/#propdef-font-variant-position .

(Alternatively, if they were intentionally omitted, there should
probably be a note that they were, since font-variant can otherwise
express everything that its longhand subproperties can except for
cases with 'font-variant-ligatures: none' mixes with non-'normal'
values on the other subproperties.)

I think the fix would be adding, after "ruby" and before the "]"
following it or elsewhere in that [ || ] expression:
  [ sub | super ]
(just like the values of font-variant-caps are in a [ | ], since
only one is allowed to be specified).

-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)