[css-tables] Clarify: CSSOM-View doesn't expose all boxes

Author: FremyCompany

css-tables-3/Overview.bs

@@ -2362,7 +2362,8 @@ spec:css-sizing-3; type:property; text:box-sizing
 			the final step of algorithm is to assign to each table-internal box its final position.
 
 		The width/height/left/top calculated below define the dimensions of the CSS Layout Box, 
-			which means that they are accessible via the <a href="https://drafts.csswg.org/cssom-view/#extensions-to-the-htmlelement-interface">offset* properties</a> defined in CSSOM-VIEW.
+			which means that they are accessible via the <a href="https://drafts.csswg.org/cssom-view/#extensions-to-the-htmlelement-interface">offset* properties</a> defined in CSSOM-VIEW,
+			(currently limited to css boxes for which you can obtain a corresponding HTMLElement reference).
 
 		The <a>table-wrapper</a> box is then sized such that
 			it contains the margin box of all <a>table-non-root</a> boxes