[css-align] Handle CSS2.1's inverted 'auto' precedence rules for abspos in ''normal'', and keep it consistent with grid/etc for all other values.

Author: tabatkins

css-align/Overview.bs

@@ -527,17 +527,17 @@ Details per Layout Mode {#distribution-details}
 			<td>
 				The entire contents of the block, as a unit.
 		<tr>
-			<th>'align-content' axis
+			<th>'align-content' Axis
 			<td>
 				The <a>block axis</a>.
 				If a <<content-distribution>> is specified
 				the <a>fallback alignment</a> is used instead.
 		<tr>
-			<th>'justify-content' axis
+			<th>'justify-content' Axis
 			<td>
 				Does not apply to and has no effect on <a>block containers</a>.
 		<tr>
-			<th>''justify-content/normal'' behavior
+			<th>''justify-content/normal'' Behavior
 			<td>
 				All values other than ''justify-content/normal'' force the block container to establish a new formatting context.
 				For table cells, the behavior of the ''justify-content/normal'' depends on the computed value of 'vertical-align':
@@ -563,17 +563,17 @@ Details per Layout Mode {#distribution-details}
 				Issue: Should this apply to column like it does grid tracks?
 				''justify-content/normal'' would act as ''stretch'', giving the current behavior.
 		<tr>
-			<th>'align-content' axis
+			<th>'align-content' Axis
 			<td>
 				The <a>block axis</a>.
 				If a <<content-distribution>> is specified
 				the <a>fallback alignment</a> is used instead.
 		<tr>
-			<th>'justify-content' axis
+			<th>'justify-content' Axis
 			<td>
 				Does not apply to and has no effect on <a>multi-column elements</a>.
 		<tr>
-			<th>''justify-content/normal'' behavior
+			<th>''justify-content/normal'' Behavior
 			<td>
 				''justify-content/normal'' behaves as ''start''.
 	</table>
@@ -594,18 +594,18 @@ Details per Layout Mode {#distribution-details}
 				For 'align-content',
 				the <a>flex lines</a>.
 		<tr>
-			<th>'align-content' axis
+			<th>'align-content' Axis
 			<td>
 				The <a>cross axis</a>.
 		<tr>
-			<th>'justify-content' axis
+			<th>'justify-content' Axis
 			<td>
 				The 'justify-content' property applies along the <a>main axis</a>,
 				but since flexing in the <a>main axis</a> is controlled by 'flex',
 				''<content-distribution>/stretch'' behaves as ''flex-start''
 				(ignoring the specified <a>fallback alignment</a>, if any).
 		<tr>
-			<th>''justify-content/normal'' behavior
+			<th>''justify-content/normal'' Behavior
 			<td>
 				''justify-content/normal'' behaves as ''<content-distribution>/stretch''.
 	</table>
@@ -624,17 +624,17 @@ Details per Layout Mode {#distribution-details}
 			<td>
 				The <a>grid tracks</a>.
 		<tr>
-			<th>'align-content' axis
+			<th>'align-content' Axis
 			<td>
 				The <a lt="block axis">block (column) axis</a>,
 				aligning the <a>grid rows</a>.
 		<tr>
-			<th>'justify-content' axis
+			<th>'justify-content' Axis
 			<td>
 				The <a lt="inline axis">inline (row) axis</a>,
 				aligning the <a>grid columns</a>.
 		<tr>
-			<th>''justify-content/normal'' behavior
+			<th>''justify-content/normal'' Behavior
 			<td>
 				''justify-content/normal'' behaves as ''stretch''.
 	</table>
@@ -859,9 +859,18 @@ Inline/Main-Axis Alignment: the 'justify-self' property</h3>
 		<tr>
 			<th>''justify-self/normal'' Behavior
 			<td>
-				Consistent with CSS2.1,
+				For consistency with CSS 2.1,
 				the ''justify-self/normal'' keyword behaves as ''start'' on replaced absolutely-positioned boxes,
 				and behaves as ''justify-self/stretch'' on all other absolutely-positioned boxes.
+
+				If the box has non-''top/auto'' offsets in this axis,
+				and either 'margin' in this axis is ''margin/auto'',
+				an ''width/auto'' 'width' is treated as ''fill-available''
+				and ''margin/auto'' margins are treated as zero.
+				(Otherwise, when 'justify-content' is not ''justify-content/normal'',
+				''width: auto'' is treated as ''width/fit-content''
+				and ''margin/auto'' margins are used for alignment
+				as in in-flow block-level layout.)
 		<tr>
 			<th>Other Details
 			<td>
@@ -880,12 +889,6 @@ Inline/Main-Axis Alignment: the 'justify-self' property</h3>
 				'justify-self' has no effect.
 	</table>
 
-	Issue: When you have non-auto left/right and auto width,
-	legacy behavior stretches the width and ignores margins.
-	We should keep "auto" around for abspos,
-	and have it do this legacy behavior.
-	Any other value (including "stretch") should do standard "auto margins get first dibs" behavior.
-
 ### Table Cells ### {#justify-cell}
 
 	This property does not apply to table cells,
@@ -976,9 +979,18 @@ Block/Cross-Axis Alignment: the 'align-self' property</h3>
 		<tr>
 			<th>''align-self/normal'' Behavior
 			<td>
-				Consistent with CSS2.1,
+				For consistency with CSS 2.1,
 				the ''align-self/normal'' keyword behaves as ''start'' on replaced absolutely-positioned boxes,
 				and behaves as ''align-self/stretch'' on all other absolutely-positioned boxes.
+
+				If the box has non-''top/auto'' offsets in this axis,
+				and either 'margin' in this axis is ''margin/auto'',
+				an ''width/auto'' 'height' is treated as ''fill-available''
+				and ''margin/auto'' margins are treated as zero.
+				(Otherwise, when 'align-content' is not ''align-content/normal'',
+				''height: auto'' is treated as ''height/fit-content''
+				and ''margin/auto'' margins are used for alignment
+				as in in-flow block-level layout.)
 		<tr>
 			<th>Other Details
 			<td>