[css-ruby] spanning of ruby annotations across excess bases

http://dev.w3.org/csswg/css-ruby/#base-annotation-pairing says:
  # If there are not enough ruby annotations in a ruby annotation
  # container, the last one is paired with (spans across) any excess
  # ruby bases. (If there are not any in the ruby annotation
  # container, an anonymous empty one is assumed to exist.)

Is there actually a use case for this behavior, or is it really just
defining error handling?

I ask because I think it adds substantial extra complexity,
especially around line-breaking of ruby.  If there isn't a good use
case for it, I would prefer if ruby annotation containers that do
not have enough annotations simply not provide annotations for the
final bases, instead of having their final annotation span all the
remaining bases.

-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)