[cssom-view-1] Per WG resolution, include fragments from block splitters unless they're zero-sized. #6588

Author: tabatkins

cssom-view-1/Overview.bs

@@ -1404,6 +1404,11 @@ The <dfn attribute for=HTMLElement>offsetWidth</dfn> attribute must return the r
     of all fragments generated by the element's [=principal box=],
     ignoring any <a>transforms</a> that apply to the element and its ancestors.
 
+    If the element's [=principal box=] is an [=inline-level box=]
+    which was "split" by a [=block-level=] descendant,
+    also include fragments generated by the [=block-level=] descendants,
+    unless they are zero width or height.
+
 The <dfn attribute for=HTMLElement>offsetHeight</dfn> attribute must return the result of running these steps:
 
 1. If the element does not have any associated <a>CSS layout box</a> return zero and terminate this algorithm.
@@ -1412,6 +1417,11 @@ The <dfn attribute for=HTMLElement>offsetHeight</dfn> attribute must return the
     of all fragments generated by the element's [=principal box=],
     ignoring any <a>transforms</a> that apply to the element and its ancestors.
 
+    If the element's [=principal box=] is an [=inline-level box=]
+    which was "split" by a [=block-level=] descendant,
+    also include fragments generated by the [=block-level=] descendants,
+    unless they are zero width or height.
+
 
 <h2 id=extensions-to-the-htmlimageelement-interface>Extensions to the {{HTMLImageElement}} Interface</h2>