[css-sizing-4] Add contain-intrinsic-size: auto none syntax (#8989)

Co-authored-by: Tab Atkins Jr. <jackalmage@gmail.com>

Author: vmpstr

css-sizing-4/Overview.bs

@@ -213,7 +213,7 @@ Preferred Aspect Ratios: the 'aspect-ratio' property</h3>
 
 		<dt><dfn>auto && <<ratio>></dfn>
 		<dd>
-			If both ''auto'' and a <<ratio>> are specified together,
+			If both ''aspect-ratio/auto'' and a <<ratio>> are specified together,
 			the [=preferred aspect ratio=] is the specified ratio
 			of ''<var>width</var> / <var>height</var>''
 			unless it is a [=replaced element=] with a [=natural aspect ratio=],
@@ -520,7 +520,7 @@ Overriding Contained Intrinsic Sizes: the 'contain-intrinsic-*' properties</h3>
 
 	<pre class=propdef>
 	Name: contain-intrinsic-width, contain-intrinsic-height, contain-intrinsic-block-size, contain-intrinsic-inline-size
-	Value: none | <<length>> | auto <<length>>
+	Value: auto? [ none | <<length>> ]
 	Initial: none
 	Inherited: no
 	Logical property group: contain-intrinsic-size
@@ -543,32 +543,26 @@ Overriding Contained Intrinsic Sizes: the 'contain-intrinsic-*' properties</h3>
 	would still size according to the specified grid,
 	usually ending up with a larger content size than specified.
 
-	Values are defined as:
-
 	<dl dfn-type=value dfn-for="contain-intrinsic-width, contain-intrinsic-height, contain-intrinsic-block-size, contain-intrinsic-inline-size, contain-intrinsic-size">
-		: <dfn>none</dfn>
-		:: The corresponding axis does not have an [=explicit intrinsic inner size=].
-
-		: <dfn><<length>></dfn>
-		:: The corresponding axis has an [=explicit intrinsic inner size=] of the specified <<length>>.
-
-		<wpt pathprefix="css/css-contain/">
-		content-visibility/content-visibility-058.html
-		</wpt>
-
-		: <dfn>auto <<length>></dfn>
-		:: If the element has a [=last remembered size=]
+		: <dfn>auto</dfn>? [ <dfn>none</dfn> | <<length>> ]
+		:: If ''contain-intrinsic-size/auto'' is specified
+			and the element has a [=last remembered size=]
 			and is currently [=skipping its contents=],
-			its [=explicit intrinsic inner size=]
-			is the [=last remembered size=].
-
+			its [=explicit intrinsic inner size=] in the corresponding axis
+			is the [=last remembered size=] in that axis.
+			
 			Note: This occurs, for example,
 			when an element with ''content-visibility: auto''
 			is off-screen.
 
 			Otherwise,
-			its [=explicit intrinsic inner size=]
-			is the specified <<length>>.
+			the corresponding axis either doesn't have an [=explicit intrinsic inner size=]
+			(if ''contain-intrinsic-size/none'' is specified)
+			or has an [=explicit intrinsic inner size=] of the specified <<length>>.
+
+			<wpt pathprefix="css/css-contain/">
+			content-visibility/content-visibility-058.html
+			</wpt>
 	</dl>
 
 	If an element has an [=explicit intrinsic inner size=] in an axis,
@@ -596,7 +590,7 @@ Overriding Contained Intrinsic Sizes: the 'contain-intrinsic-*' properties</h3>
 
 	<pre class="propdef shorthand">
 	Name: contain-intrinsic-size
-	Value: [ none | <<length>> | auto <<length>> ]{1,2}
+	Value: [ auto? [ none | <<length>> ] ]{1,2}
 	</pre>
 
 	'contain-intrinsic-size' is a shorthand property
@@ -619,7 +613,7 @@ Last Remembered Size</h4>
 	even slightly,
 	it can cause unsightly scrollbars or accidentally-hidden content.
 
-	The ''contain-intrinsic-size: auto'' value allows a middle-ground:
+	The ''contain-intrinsic-size/auto'' keyword of ''contain-intrinsic-size'' allows a middle-ground:
 	if an element is ever <em>not</em> [=size containment|size-contained=],
 	this value causes the element to remember its size
 	(calculated as normal by layout);
@@ -634,20 +628,20 @@ Last Remembered Size</h4>
 		The [=last remembered size=] of an element is determined by:
 
 		* At the time that {{ResizeObserver}} events are determined and delivered,
-			if an element has ''contain-intrinsic-size: auto'',
+			if an element has a ''contain-intrinsic-size/auto'' keyword in ''contain-intrinsic-size'' property,
 			is capable of being a {{ResizeObserver}} target,
 			but does not have [=size containment=],
 			record the current inner dimensions of its [=principal box=]
 			as its [=last remembered size=].
 
 		* At the time that {{ResizeObserver}} events are determined and delivered,
 			if an element has a [=last remembered size=]
-			but does <em>not</em> have ''contain-intrinsic-size: auto'',
+			but does <em>not</em> have ''contain-intrinsic-size/auto'' keyword in ''contain-intrinsic-size'' property,
 			remove its [=last remembered size=].
 
 		Note: The [=last remembered size=] is state attached to the <em>element</em>,
 		not any particular box generated by the element.
-		So long as the element retains ''contain-intrinsic-size: auto'',
+		So long as the element retains ''contain-intrinsic-size/auto'' keywrod in ''contain-intrinsic-size'' property,
 		it will remember its [=last remembered size=]
 		even across changes such as going to/from ''display: none''.
 	</div>
@@ -995,6 +989,7 @@ Recent Changes</h3>
 	* Fixed some errors in the [[#aspect-ratio-size-transfers]] section,
 		aligning the behavior to not conflict with behavior defined by CSS2 / CSS Flex Layout / etc.
 		(<a href="https://github.com/w3c/csswg-drafts/issues/6071">Issue 6071</a>)
+	* Added ''contain-intrinsic-size: auto none'' syntax.
 
 	Significant changes since the <a href="https://www.w3.org/TR/2020/WD-css-sizing-4-20200526/">26 May 2020 First Public Working Draft</a> include: