[css-sizing-4] Replace the intrinsic-* properties with contain-intrin…

…sic-size, per WG resolution. Closes w3c#4531.

css-sizing-4/Overview.bs

@@ -612,69 +612,57 @@ Max-content Sizes in Constrained-height Multi-column Layout</h3>
 
 
 <h3 id='intrinsic-size-override'>
-Overriding Intrinsic Sizes: the 'intrinsic-*' properties</h3>
+Overriding Contained Intrinsic Sizes: the 'contain-intrinsic-size' property</h3>
 
 	<pre class="propdef">
-	Name: intrinsic-block-size, intrinsic-inline-size, intrinsic-height, intrinsic-width
-	Value: legacy | auto | <<length>>
-	Initial: legacy
+	Name: contain-intrinsic-size
+	Value: none | <<length>>{1,2}
+	Initial: none
 	Inherited: no
-	Applies to: all elements except [=non-replaced=] [=inlines=]
-	Computed value: as specified, with <<length-percentage>> values computed
+	Applies to: elements with [=size containment=]
+	Computed value: as specified, with <<length>> values computed
 	Percentages: n/a
 	Animation type: by computed value type
 	</pre>
-
-	The 'intrinsic-*' properties determine
-	whether the [=intrinsic sizes=] of a box
-	are calculated from sizes derived from its content
-	(as defined by the rest of this chapter),
-	or from a specified <dfn export>explicit intrinsic inner size</dfn>.
-	Values are defined as follows:
-
-	<dl dfn-type=value dfn-for="intrinsic-block-size, intrinsic-inline-size, intrinsic-height, intrinsic-width, intrinsic-size">
-		: <dfn>legacy</dfn>
-		::
-			Does not specify an [=explicit intrinsic inner size=] of the box
-			in the relevant axis.
-			(Intrinsic sizes are thus determined in various ways
-			based on examining the content of the box as usual.
-			See [[#intrinsic]], for example.)
-
-
-		: <dfn>auto</dfn>
+
+	This property allows elements with [=size containment=] to specify
+	an <dfn export>explicit intrinsic inner size</dfn>,
+	causing the box to size as if it had contents
+	with a combined width and height
+	matching the specified [=explicit intrinsic inner size=]
+	(rather than sizing as if it were empty).
+
+	Note: An element with [=size containment=] is laid out as if it had no contents [[!CSS-CONTAIN-1]],
+	which in many cases this will cause the element to collapse to zero inner height.
+	This can be corrected with an explicit 'height' chosen to show the expected contents,
+	but that can have unintended effects in some layout systems,
+	such as Flex and Grid Layout,
+	which treat an explicit 'height' as a stronger command
+	than an implicit content-based height.
+	The element thus might lay out substantially differently than it would have
+	were it simply filled with content up to that height.
+	Providing an [=explicit intrinsic inner size=] for the element
+	preserves the performance benefits of ignoring its contents for layout
+	while still allowing it to size as if it had content.
+
+	Values are defined as:
+
+	<dl dfn-type=value dfn-for="contain-intrinsic-size">
+		: <dfn>none</dfn>
 		::
-			If 'overflow' is not ''visible'' in the relevant axis,
-			specifies a zero [=explicit intrinsic inner size=]
-			in that axis.
-			Otherwise same as ''legacy''.
+			Does not specify an [=explicit intrinsic inner size=]
+			for elements with [=size containment=].
 
-		: <dfn><<length>></dfn>
+		: <dfn><<length>>{2}</dfn>
 		::
-			Specifies an [=explicit intrinsic inner size=]
-			in the relevant axis.
+			If the element has [=size containment=],
+			specifies an [=explicit intrinsic inner size=].
+			The first <<length>> provides the inner width of the element,
+			the second provides the inner height.
+			If the second <<length>> is omitted,
+			it defaults to the same value as the first.
 	</dl>
 
-	Note: The value of 'intrinsic-*' in one axis has no affect on the other axis.
-
-	<pre class="propdef shorthand">
-	Name: intrinsic-size
-	Value: <<'intrinsic-width'>> <<'intrinsic-height'>>?
-	</pre>
-
-	The 'intrinsic-size' property is a [=shorthand=]
-	for setting all the 'intrinsic-*' properties in one declaration.
-
-	The first value sets 'intrinsic-width',
-	and the second value sets 'intrinsic-height'.
-	If the second value is omitted,
-	it defaults to the first.
-
-	Issue: When we figure out how to make other physical x/y shorthands,
-	like 'background-size',
-	work with logical sizes,
-	we'll apply the same logic here.
-
 
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