[css-box-4] Introduce terms for shaped/unshaped box edges #5132

Author: fantasai

css-box-4/Overview.bs

@@ -189,6 +189,14 @@ Boxes and Edges {#box-edges}
 			and <a>margin areas</a>.
 	</dl>
 
+	Properties like 'border-radius' can change the shape of the box’s [=edges=]
+	as used for painting and clipping (see [[css-backgrounds-3#corner-clipping]]);
+	these effects typically do not affect layout however.
+	To distinguish, specifications can refer to the relevant
+	<dfn export lt="shaped edge | shaped content edge | shaped padding edge | shaped border edge | shaped margin edge">shaped edge</dfn>
+	or
+	<dfn export lt="unshaped edge | unshaped content edge | unshaped padding edge | unshaped border edge | unshaped margin edge">unshaped edge</dfn>
+
 Fragmentation {#fragmentation}
 -------------