[css-shapes] update interpolation section

Author: astearns

css-shapes/Overview.html

@@ -530,45 +530,25 @@ <h3 class="heading settled heading" data-level=3.2 id=basic-shape-interpolation>
 
 <p>	<ul>
 		<li>
-			If both basic shapes are of the same type
-			and not of type polygon:
-			<ul>
-				<li>Interpolate between each value.</li>
-			</ul>
-		</li>
-		<li>
-			If one basic shape is of type rectangle
-			and the second of type circle or ellipse:
+			For interpolating between two shapes that are type inset-rectangle, ellipse or circle:
 			<ul>
 				<li>
-					Replace the circle/ellipse with
-					a temporary rectangle of equal dimension.
+					Replace each inset-rectangle with a temporary inset-rectangle with offsets relative to the margin-box.
 				</li>
 				<li>
-					Set the values for rx and ry
-					on the temporary rectangle to ‘50%’.
+					Replace each circle and ellipse with a temporary inset-rectangle with offsets relative to the margin-box, and &lt;<a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-backgrounds-4/#border-radius title=border-radius>border-radius</a>&gt; values to make the inset-rectangle equivalent to the original circle or ellipse
 				</li>
 				<li>
-					Interpolate between the two rectangles as above.
+					Interpolate between each value of the temporary inset-rectangles.
 				</li>
 			</ul>
 		</li>
-		<li>
-			If one basic shape is an inset rectangle
-			and the second is of type rectangle, circle or ellipse:
-			<ul>
-				<li>
-					Replace the inset rectangle with
-					a temporary rectangle of equal dimension.
-				</li>
-				<li>
-					Interpolate between the basic shapes as above.
-				</li>
-			</ul>
 		<li>
 			If both basic shapes are of type polygon
 			and if both polygons have the same number of vertices:
 			<ul>
+				<li>
+					If the polygons use a different relevant box, replace one of the polygons with a temporary equivalent polygon that uses the relevant box of the other.
 				<li>
 					Interpolate between each value.
 				</li>

css-shapes/Overview.src.html

@@ -413,45 +413,25 @@ <h3 id='basic-shape-interpolation'>
 
 	<ul>
 		<li>
-			If both basic shapes are of the same type
-			and not of type polygon:
-			<ul>
-				<li>Interpolate between each value.</li>
-			</ul>
-		</li>
-		<li>
-			If one basic shape is of type rectangle
-			and the second of type circle or ellipse:
+			For interpolating between two shapes that are type inset-rectangle, ellipse or circle:
 			<ul>
 				<li>
-					Replace the circle/ellipse with
-					a temporary rectangle of equal dimension.
+					Replace each inset-rectangle with a temporary inset-rectangle with offsets relative to the margin-box.
 				</li>
 				<li>
-					Set the values for rx and ry
-					on the temporary rectangle to ‘50%’.
+					Replace each circle and ellipse with a temporary inset-rectangle with offsets relative to the margin-box, and <'border-radius'> values to make the inset-rectangle equivalent to the original circle or ellipse
 				</li>
 				<li>
-					Interpolate between the two rectangles as above.
+					Interpolate between each value of the temporary inset-rectangles.
 				</li>
 			</ul>
 		</li>
-		<li>
-			If one basic shape is an inset rectangle
-			and the second is of type rectangle, circle or ellipse:
-			<ul>
-				<li>
-					Replace the inset rectangle with
-					a temporary rectangle of equal dimension.
-				</li>
-				<li>
-					Interpolate between the basic shapes as above.
-				</li>
-			</ul>
 		<li>
 			If both basic shapes are of type polygon
 			and if both polygons have the same number of vertices:
 			<ul>
+				<li>
+					If the polygons use a different relevant box, replace one of the polygons with a temporary equivalent polygon that uses the relevant box of the other.
 				<li>
 					Interpolate between each value.
 				</li>