[css-sizing-4] Define the intrinsic-* family of sizing properties. Closes w3c#4229.

Author: tabatkins

css-sizing-4/Overview.bs

@@ -604,6 +604,104 @@ Max-content Sizes in Constrained-height Multi-column Layout</h3>
 		this approximation collapses to simply doing a layout,
 		and measuring the resulting columns.
 
+
+
+<h2 id="intrinsic-contribution">
+Intrinsic Size Contributions</h2>
+
+	A box’s <a>min-content contribution</a>/<a>max-content contribution</a> in each axis
+	is the size of the content box
+	of a hypothetical ''width/auto''-sized float
+	that contains only that box,
+	if that hypothetical float's containing block is zero-sized/infinitely-sized.
+
+	However, if the box has an [=explicit intrinsic inner size=] in an axis,
+	then the box's [=automatic size=] in that axis
+	is calculated by assuming the [=explicit intrinsic inner size=]
+	as its [=inner size=] in that axis.
+
+	Note: This specification does not define precisely how to determine these sizes.
+	Please refer to [[CSS2]],
+	the relevant CSS specification for that display type,
+	the <a href="#percentage-sizing">rules for handling percentages</a> (below),
+	and/or existing implementations
+	for further details.
+
+
+<h3 id='intrinsic-size-override'>
+Overriding Intrinsic Sizes: the 'intrinsic-*' properties</h3>
+
+	<pre class="propdef">
+	Name: intrinsic-block-size, intrinsic-inline-size, intrinsic-height, intrinsic-width
+	Value: legacy | auto | <<length-percentage>>
+	Initial: legacy
+	Inherited: no
+	Applies to: all elements except [=non-replaced=] [=inlines=]
+	Computed value: as specified, with <<length-percentage>> values computed
+	Percentages: relative to width/height of [=containing block=]
+	Animation type: by computed value type
+	</pre>
+
+	The 'intrinsic-*' properties determine
+	whether the [=intrinsic size contributions=] of a box
+	are calculated from sizes derived from its content
+	or from a specified <dfn export>explicit intrinsic inner size</dfn>.
+	See [[#intrinsic-contribution]].
+	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 size contribution are thus determined in various ways
+			based on examining the content of the box as usual.
+			See [[#intrinsic]], for example.)
+
+
+		: <dfn>auto</dfn>
+		::
+			If 'overflow' is not ''visible'' in the relevant axis,
+			specifies a zero [=explicit intrinsic inner size=]
+			in that axis.
+			Otherwise same as ''legacy''.
+
+		: <dfn><<length-percentage>></dfn>
+		::
+			Specifies an [=explicit intrinsic inner size=]
+			in the relevant axis.
+	</dl>
+
+	<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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+
 <h2 id='extrinsic'>
 Extrinsic Size Determination</h2>