[css-break] generated box -> principal box

Author: fantasai

css-break/Overview.html

@@ -746,7 +746,7 @@ <h3 id=break-within><span class=secno>3.2. </span> Breaks Within Boxes: the
   </table>
 
   <p> This property specifies page/column/region break behavior within the
-   generated box. Values have the following meanings:
+   element's principal box. Values have the following meanings:
 
   <dl>
    <dt>‘<code class=css>auto</code>’

css-break/Overview.src.html

@@ -453,7 +453,7 @@ <h3 id="break-within">
 
   <p>
     This property specifies page/column/region break behavior
-    within the generated box.
+    within the element's principal box.
     Values have the following meanings:
 
   <dl>