[css-position-3] Add a note to 'inset' about it resolving against the physical longhands.

Author: tabatkins

css-position-3/Overview.bs

@@ -99,7 +99,7 @@ Link Defaults: css-transforms-1 (property) transform
 </style>
 
 <pre class=anchors>
-urlPrefix: https://www.w3.org/TR/CSS2/visuren.html; spec: CSS2; 
+urlPrefix: https://www.w3.org/TR/CSS2/visuren.html; spec: CSS2;
 	url: #normal-flow; text: normal flow; type: dfn;
 	url: #x1; text: viewport; type: dfn;
 urlPrefix: https://www.w3.org/TR/CSS21/media.html; spec: CSS2;
@@ -130,7 +130,7 @@ Introduction</h2>
 	* [=Sticky positioning=], which visually shifts a box relative to its laid-out location
 		in order to keep it visible when a scrollable ancestor
 		would otherwise scroll it out of sight.
-	* [=Absolute positioning=], which ignores normal layout entirely, 
+	* [=Absolute positioning=], which ignores normal layout entirely,
 		pulling the element [=out of flow=] and
 		positioning it relative to its [=containing block=]
 		with no regard for other content.
@@ -150,7 +150,7 @@ Introduction</h2>
 <h3 id="placement">
 Module Interactions</h3>
 
-	This module replaces and extends the [=positioning scheme=] features 
+	This module replaces and extends the [=positioning scheme=] features
 	defined in [[!CSS2]] sections:
 
 	<ul>
@@ -326,7 +326,7 @@ Containing Blocks of Positioned Boxes</h3>
 			</dl>
 
 			If no ancestor establishes one,
-			the [=absolute positioning containing block=] is 
+			the [=absolute positioning containing block=] is
 			the [=initial containing block=].
 
 			Note: Properties that can cause a box to establish
@@ -489,7 +489,7 @@ Box Insets: the 'top', 'right', 'bottom', 'left', 'inset-block-start', 'inset-in
 			in the corresponding axis
 			(e.g. width for 'left' or 'right', height for 'top' and 'bottom').
 			For [=sticky positioned=] boxes,
-			the inset is instead 
+			the inset is instead
 			relative to the relevant [=scrollport=]’s size.
 			Negative values are allowed.
 
@@ -544,6 +544,22 @@ Box Insets Shorthands: the 'inset-block', 'inset-inline', and 'inset' properties
 	assigning values to the longhands representing each side
 	exactly as the 'margin' property does for its longhands.
 
+	<div class=note>
+
+		By default, the 'inset' property values
+		are assigned to the corresponding <em>[=physical=]</em> [=longhand properties=]--
+		'top', 'right', 'bottom', and 'left'--
+		which for historical reasons do not have an <css>inset-</css> prefix.
+		This matches the behavior of other "4 values assigned to sides" properties,
+		such as 'margin'.
+
+		Allowing properties such as this to resolve to the [=flow-relative=] [=longhands=] is under discussion in [[CSS-LOGICAL-1]].
+
+		Yes, we understand it's a little confusing
+		that 'inset' doesn't expand to any 'inset-*' properties.
+	</div>
+
+
 
 <h3 id="relpos-insets" oldids="relpos">
 Relative Positioning</h3>
@@ -607,7 +623,7 @@ Sticky positioning</h3>
 	in reference to the [=nearest scrollport=].
 
 	For a [=sticky positioned=] [=box=],
-	the [=inset properties=] 
+	the [=inset properties=]
 	represent insets from the respective edges of the [=nearest scrollport=],
 	defining the <dfn export>sticky view rectangle</dfn>
 	used to constrain the box’s position.
@@ -670,7 +686,7 @@ Scroll Position of Sticky-Positioned Boxes</h4>
 		For example, if a user clicks a link targetting a [=sticky-positioned=] element,
 		even if the element's [=nearest scrollport=] is currently scrolled
 		such that the [=sticky positioned=] element is offset from its initial position,
-		the [=scrollport=] will be scrolled back 
+		the [=scrollport=] will be scrolled back
 		so that the element's initial position is visible.
 	</div>
 
@@ -712,7 +728,7 @@ Absolute (and Fixed) Positioning</h3>
 			(<var>containing block size</var> - 2 &times; |<var>start distance</var>|);
 			otherwise,
 			set the end-edge [=inset property=] to zero
-			and the start-edge [=inset property=] to 
+			and the start-edge [=inset property=] to
 			(<var>containing block size</var> - 2 &times; |<var>end distance</var>|).
 	</dl>
 
@@ -1162,7 +1178,7 @@ The width of absolute or fixed positioned, replaced elements</h3>
 
 		<li>
 		If at this point the values are over-constrained,
-		ignore the value for either 'left' 
+		ignore the value for either 'left'
 		(in case the 'direction' property of the <a>containing block</a> is ''rtl'')
 		or 'right' (in case 'direction' is ''ltr'')
 		and solve for that value.
@@ -1171,8 +1187,8 @@ The width of absolute or fixed positioned, replaced elements</h3>
 <h3 id="abs-non-replaced-height">
 The Height Of Absolutely Positioned, Non-Replaced Elements</h3>
 
-	For absolutely positioned elements, 
-	the used values of the vertical dimensions 
+	For absolutely positioned elements,
+	the used values of the vertical dimensions
 	must satisfy this constraint:
 
 	<code>
@@ -1181,95 +1197,95 @@ The Height Of Absolutely Positioned, Non-Replaced Elements</h3>
 		= <span>height of containing block</span>
 	</code>
 
-	If all three of 'top', 'height', and 'bottom' are ''top/auto'': 
-	First set any ''top/auto'' values for 'margin-top' and 'margin-bottom' to ''0'', 
-	then set 'top' to the static position, 
+	If all three of 'top', 'height', and 'bottom' are ''top/auto'':
+	First set any ''top/auto'' values for 'margin-top' and 'margin-bottom' to ''0'',
+	then set 'top' to the static position,
 	and finally apply rule number <em>three</em> below.
 
-	If none of the three are ''top/auto'': 
+	If none of the three are ''top/auto'':
 	If both 'margin-top' and 'margin-bottom' are ''top/auto'',
-	solve the equation under the extra constraint that the two margins get equal values. 
-	If one of 'margin-top' or 'margin-bottom' is ''top/auto'', 
-	solve the equation for that value. 
-	If the values are over-constrained, 
+	solve the equation under the extra constraint that the two margins get equal values.
+	If one of 'margin-top' or 'margin-bottom' is ''top/auto'',
+	solve the equation for that value.
+	If the values are over-constrained,
 	ignore the value for 'bottom' and solve for that value.
 
-	Otherwise, 
-	set ''top/auto'' values for 'margin-top' and 'margin-bottom' to ''0'', 
+	Otherwise,
+	set ''top/auto'' values for 'margin-top' and 'margin-bottom' to ''0'',
 	and pick one of the following six rules that apply.
 
 	1. If 'top' and 'height' are ''top/auto''
-		and 'bottom' is not ''top/auto'', 
-		then the height is based on the 
+		and 'bottom' is not ''top/auto'',
+		then the height is based on the
 		<a href="https://www.w3.org/TR/CSS2/visudet.html#root-height">Auto heights for block formatting context roots</a>,
 		and solve for 'top'.
 
-	2. If 'top' and 'bottom' are ''top/auto'' 
-		and 'height' is not ''top/auto'', 
-		then set 'top' to the static position, 
+	2. If 'top' and 'bottom' are ''top/auto''
+		and 'height' is not ''top/auto'',
+		then set 'top' to the static position,
 		then solve for 'bottom'.
 
-	3. If 'height' and 'bottom' are ''top/auto'' 
-		and 'top' is not ''top/auto'', 
-		then the height is based on the 
+	3. If 'height' and 'bottom' are ''top/auto''
+		and 'top' is not ''top/auto'',
+		then the height is based on the
 		<a href="https://www.w3.org/TR/CSS2/visudet.html#root-height">Auto heights for block formatting context roots</a>,
 		and solve for 'bottom'.
 
-	4. If 'top' is ''top/auto'', 
-		'height' and 'bottom' are not ''top/auto'', 
+	4. If 'top' is ''top/auto'',
+		'height' and 'bottom' are not ''top/auto'',
 		then solve for 'top'.
 
-	5. If 'height' is ''top/auto'', 
-		'top' and 'bottom' are not ''top/auto'', 
+	5. If 'height' is ''top/auto'',
+		'top' and 'bottom' are not ''top/auto'',
 		then solve for 'height'.
 
-	6. If 'bottom' is ''top/auto'', 
-		'top' and 'height' are not ''top/auto'', 
+	6. If 'bottom' is ''top/auto'',
+		'top' and 'height' are not ''top/auto'',
 		then solve for 'bottom'.
 
 <h3 id="abs-replaced-height">
 The Height Of Absolutely Positioned, Replaced Elements</h3>
 
-	If 'height' and 'width' both have computed values of ''top/auto'' 
-	and the element also has an intrinsic height, 
+	If 'height' and 'width' both have computed values of ''top/auto''
+	and the element also has an intrinsic height,
 	then that intrinsic height is the used value of 'height'.
 
-	Otherwise, if 'height' has a computed value of ''top/auto'' 
-	and the element has an intrinsic ratio 
+	Otherwise, if 'height' has a computed value of ''top/auto''
+	and the element has an intrinsic ratio
 	then the used value of 'height' is:
 
 	<code>(used width) / (intrinsic ratio)</code></p>
 
-	Otherwise, if 'height' has a computed value of ''top/auto'' 
-	and the element has an intrinsic height, 
+	Otherwise, if 'height' has a computed value of ''top/auto''
+	and the element has an intrinsic height,
 	then that intrinsic height is the used value of 'height'.
 
-	Otherwise, if 'height' has a computed value of ''top/auto'', 
-	but none of the conditions above are met, 
-	then the used value of 'height' must be set to 
-	the height of the largest rectangle that has a 2:1 ratio, 
-	has a height not greater than ''150px'', 
+	Otherwise, if 'height' has a computed value of ''top/auto'',
+	but none of the conditions above are met,
+	then the used value of 'height' must be set to
+	the height of the largest rectangle that has a 2:1 ratio,
+	has a height not greater than ''150px'',
 	and has a width not greater than the device width.
 
-	After establishing the 'height', 
-	in order to position the replaced element, 
+	After establishing the 'height',
+	in order to position the replaced element,
 	apply the following rules as appropriate.
 
-	1. If both 'top' and 'bottom' have the value ''top/auto'', 
+	1. If both 'top' and 'bottom' have the value ''top/auto'',
 		replace 'top' with the element’s static position.
 
-	2. If 'bottom' is ''top/auto'', 
+	2. If 'bottom' is ''top/auto'',
 		replace any ''top/auto'' on 'margin-top' or 'margin-bottom'
 		with ''0''.
 
 	3. If at this point both 'margin-top' and 'margin-bottom' are still ''top/auto'',
-		solve the equation under the extra constraint 
+		solve the equation under the extra constraint
 		that the two margins must get equal values.
 
-	4. If at this point there is only one ''top/auto'' remaining, 
+	4. If at this point there is only one ''top/auto'' remaining,
 		solve the equation for that value.
 
-	5. If at this point the values are over-constrained, 
+	5. If at this point the values are over-constrained,
 		ignore the value for 'bottom' and solve for that value.
 
 <h2 id="comparison">