[css-sizing-4] Stash modified preferred aspect ratio definition to merge in later.

Author: fantasai

css-sizing-4/Overview.bs

@@ -77,6 +77,19 @@ Terminology</h2>
 
 Issue: [[css-sizing-3#terms]]
 
+<!-- merge this with the final sizing-3 definition
+<dt><dfn export>preferred aspect ratio</dfn>
+<dd>
+    A [=box=] or [=replaced element=]’s preferred ratio of width to height.
+    This can be explicitly specified via the 'aspect-ratio' property,
+    or, for replaced elements, it can be an [=intrinsic aspect ratio=]
+    derived from the content.
+    The [=preferred aspect ratio=] of a box can be associated
+    with either its [=content box=] or [=border box=].
+    Not all boxes or replaced elements have a [=preferred aspect ratio=]
+    (and in fact, non-replaced elements typically do not).
+-->
+
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