[css-backgrounds-3][css-borders-4] Fixed definition for where box shadows apply

Author: SebastianZ

css-backgrounds-3/Overview.bs

@@ -28,6 +28,7 @@ spec:css2; type:value; text:inline-table
 spec:css2; type:value; text:table-cell
 spec:css2; type:property; text:overflow
 spec:css2; type:value; text:visible
+spec:css-break-4; type:dfn; text:fragment
 spec:css-color-3; type:property; text:color
 spec:css-color-3; type:value; text:transparent
 spec:selectors-3; type:selector; text: ::first-letter
@@ -2504,7 +2505,8 @@ Layering, Layout, and Other Details</h4>
   and the <i>inner shadows</i> of an element are drawn immediately above the background of that element
   (below the borders and border image, if any).
 
-  <p>If an element has multiple boxes, all of them get drop shadows,
+  <p>Drop shadows are only applied to the [=principal box=].
+  If that box has multiple [=fragments=], then all of them get shadows,
   but shadows are only drawn where borders would also be drawn;
   see 'box-decoration-break'.
 
@@ -2599,6 +2601,8 @@ Changes since the 14 February 2024 Candidate Recommendation Snapshot</h3>
     (<a href="https://github.com/w3c/csswg-drafts/issues/8496">Issue 8496</a>)
   <li>Fixed an error in the Computed Value line of 'background-image'.
     (<a href="https://github.com/w3c/csswg-drafts/issues/8604">Issue 8604</a>)
+  <li>Fixed the definition for where box shadows apply.
+    (<a href="https://github.com/w3c/csswg-drafts/issues/9286">Issue 9286</a>)
 </ul>
 
 

css-borders-4/Overview.bs

@@ -791,7 +791,8 @@ Layering, Layout, and Other Details</h4>
   and the <i>inner shadows</i> of an element are drawn immediately above the background of that element
   (below the borders and border image, if any).
 
-  <p>If an element has multiple boxes, all of them get drop shadows,
+  <p>Drop shadows are only applied to the [=principal box=].
+  If that box has multiple [=fragments=], then all of them get shadows,
   but shadows are only drawn where borders would also be drawn;
   see 'box-decoration-break'.