[css-ruby][css-text-decor] Text-decoration on ruby

It is not clear how text decorations should be rendered on ruby elements,
or more specifically, what should happen on sides of short base text with
long annotation?

For example, if we have content like:

<ruby>base 1<rt>a very very very long annotation</rt>base 2<rt>another very
very very long annotation</rt></ruby>

then we specify "text-decoration: underline" to <ruby> or some of its
inline ancestors. What should happen? Currently, WebKit and Blink and
Trident won't draw the underline in the gap between the bases, and between
text preceding/following and the ruby, while Gecko will draw lines in those
places. More precisely, Gecko currently extends the decoration lines to the
boundary of each box, other impls don't do that.

It seems to me that our (Gecko) impl makes more sense if the ruby is part
of a sentence, while other impls make more sense when ruby is put alone as
a single word.

This problem becomes more complicated when considering the different values
of ruby-align. I guess users of "center" and "start" probably don't want to
extend the lines to the boundary of boxes.

Any idea?

- Xidorn