[css-ruby] wording of line spacing rules

A few comments on http://dev.w3.org/csswg/css-ruby/#line-height ,
the section on how ruby affects line spacing.

  # However, if the line-height specified on the ruby container is
  # less than the distance between the top of the top ruby
  # annotation container and the bottom of the bottom ruby
  # annotation container, then additional leading is added on the
  # appropriate side of the ruby base container

This needs to say what definition of "top" it's using.  In inline
layout both top margin edge and top of font + leading are frequently
used, although in this case it might actually mean the top of an
anonymous block (or line) sized around the ruby as though it is an
inline (which would include the line-height of descendants as well).
It could mean one of these, or something else.  Which is chosen
affects whether 'line-height' on display:ruby-text-container and
(separately) on display:ruby-text has any effect.

  # such that if a block consisted of three lines each containing
  # ruby identical to this, none of the ruby containers would
  # overlap. 

It's not clear to me that there's a clear position and size defined
for the ruby container, such that it's clear what it means for them
to overlap.  Does this mean to say "none of the ruby base containers
and ruby annotation containers would overlap"?  It should also
probably be clearer, again, on which definitions of top and bottom
are being used.

It might also be better to define the amount of leading added, which
would make it clearer, for example, that this rule on preventing
overlap applies before relative positioning.

-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)