[css-overflow-3] Make 'clip' reference non-exhaustive. Fix links.

Author: fantasai

css-overflow-3/Overview.bs

@@ -154,8 +154,8 @@ Scrollable overflow</h3>
 			the border boxes
 			of all boxes for which it is the containing block,
 			accounting for transforms by projecting each box onto
-			the plane of the element that establishes its <a>3d-rendering context</a>.
-			[[!CSS-TRANSFORMS-1]]
+			the plane of the element that establishes its <a>3D rendering context</a>.
+			[[!CSS3-TRANSFORMS]]
 
 			Issue: Is this description of handling transforms
 			sufficiently accurate?
@@ -165,8 +165,8 @@ Scrollable overflow</h3>
 			(accounting for transforms as described above),
 			provided they themselves have ''overflow: visible''
 			(i.e. do not themselves trap the overflow)
-			and that overflow is not already clipped
-			by the 'clip' property.
+			and that <a>scrollable overflow</a> is not already clipped
+			(e.g. by the 'clip' property or the 'contain' property).
 
 			Note: The 'mask-*' properties [[!CSS-MASKING-1]]
 			do not affect the <a>scrollable overflow region</a>.