Add a note about the future of ruby

Fixes #264.
Closes #347.

index.bs

@@ -1510,6 +1510,10 @@ underlined text, and a <a>WebVTT cue span end tag</a> "<code>u</code>".</p>
 <p class="note">Cue positioning controls the positioning of the baseline text, not the ruby
 text.</p>
 
+<p class="note">Ruby in WebVTT is a subset of the ruby features in HTML. This might be extended in
+the future to also support an object for ruby base text as well as complex ruby, when these features
+are more mature in HTML and CSS. [[HTML]] [[CSS3-RUBY]]</p>
+
 <p>A <dfn>WebVTT cue voice span</dfn> consists of the following components, in the order given:</p>
 
 <ol>
@@ -4540,7 +4544,7 @@ corresponding <a lt="text track cue">cue</a>'s <a>WebVTT cue text alignment</a>:
 </table>
 
 <p>The 'font' shorthand property on the (root) <a>list of WebVTT Node Objects</a> must be set to
-''5vh sans-serif''. [[!CSS3-RUBY]] [[!CSS-VALUES]]</p>
+''5vh sans-serif''. [[!CSS-VALUES]]</p>
 
 <p>The 'color' property on the (root) <a>list of WebVTT Node Objects</a> must be set to
 ''rgba(255,255,255,1)''. [[!CSS3-COLOR]]</p>