[css-ruby-1] Try to make ruby segments sentence clearer.

Author: fantasai

css-ruby-1/Overview.bs

@@ -184,7 +184,7 @@ Ruby Box Model</h2>
 		<figcaption>The Japanese compound word “上手” annotated with its pronunciation “じょうず”. Each syllable is associated individually with its base character.</figcaption>
 	</figure>
 
-	Consecutive bases and annotations are grouped together into [=ruby segments=].
+	Sets of consecutive bases and their consecutive annotations are grouped together into [=ruby segments=].
 	Within a [=ruby segment=], a [=ruby annotation=] may span multiple [=ruby bases=].
 
 	<figure>