[css-align-3] First draft of specifying effect of *-content on how to compute static position/sizing of abspos elements. #1432 (comment)

tabatkins · tabatkins · commit f6cb21b55ac0 · 2018-06-13T16:27:20.000-07:00
diff --git a/css-align-3/Overview.bs b/css-align-3/Overview.bs
@@ -20,11 +20,12 @@ Previous Version: https://www.w3.org/TR/2014/WD-css-align-3-20141218/
 Previous Version: https://www.w3.org/TR/2013/WD-css3-align-20130514/
 Previous Version: https://www.w3.org/TR/2012/WD-css3-align-20120612/
 Abstract: This module contains the features of <a href="https://www.w3.org/TR/CSS/">CSS</a> relating to the alignment of boxes within their containers in the various CSS box layout models: block layout, table layout, flex layout, and grid layout. (The alignment of text and inline-level content is defined in [[CSS-TEXT-3]] and [[CSS-INLINE-3]].)
-Ignored Terms: table cell, stretch, scrollable overflow region
+Ignored Terms: table cell, stretch, scrollable overflow region, static position, static-position containing block, static positions
 At Risk: ''[ first | last ]? baseline''
 At Risk: the <<overflow-position>> keywords
 At Risk: the scrollable-area safety trigger into ''safe'' mode when no <<overflow-position>> is specified
 At Risk: the ''legacy'' keyword for 'justify-items'
+At Risk: the effect of the <a>box alignment properties</a> on absolutely-positioned boxes with ''left/auto'' offsets
 </pre>
 
 <pre class=link-defaults>
@@ -911,7 +912,9 @@ The 'justify-content' and 'align-content' Properties</h3>
 		<tr>
 			<th>'justify-content' Axis
 			<td>
-				Does not apply to and has no effect on <a>block containers</a>.
+				Does not apply to and has no effect on <a>block containers</a>
+				except insofar as it affects absolutely-positioned elements,
+				see [[#distribution-abspos-static]].
 		<tr>
 			<th>''justify-content/normal'' Behavior
 			<td>
@@ -927,6 +930,43 @@ The 'justify-content' and 'align-content' Properties</h3>
 				''justify-content/normal'' otherwise behaves as ''start''.
 	</table>
 
+### Static Position of Absolutely-Positioned Boxes ### {#distribution-abspos-static}
+
+	When applying the layout rules for absolutely-positioned elements
+	([[CSS2#abs-non-replaced-width]] and [[CSS2#abs-replaced-width]])
+	wherever the 'direction' property of the <a>static-position containing block</a> is referenced,
+	instead reference the value of its 'justify-content' or 'align-content' property
+	(whichever is defined to apply to the <a>static-position containing block</a>’s <a>inline axis</a>),
+	treating ''justify-content/normal'' as ''start''
+	and any <a>distributed alignment</a> value as its <a>fallback alignment</a>.
+	For example,
+	when 'direction' is ''ltr'' and 'justify-content' is ''justify-content/end'',
+	apply the rules for ''direction: rtl'';
+	when 'direction' is ''rtl'' and 'justify-content' is ''justify-content/space-between'',
+	apply the rules for ''direction: rtl'';
+	etc.
+
+	For the case of ''justify-content/center'' (or its equivalent),
+	split the difference:
+	when both 'inset-inline-start' and 'inset-inline-end'
+	('left' and 'right' in horizontal LTR <a>writing modes</a>)
+	are ''left/auto'',
+	set each to its <a>static position</a>,
+	and if the resulting “shrink-to-fit” <a>inline size</a> conflicts,
+    re-solve the equation for 'inset-inline-end'.
+
+    Note: What this means is that,
+    instead of always sizing an absolutely-positioned element
+    within the available space between
+    its inline-start <a>static position</a>
+    and its inline-end <a>containing block</a> edge,
+    the author can choose to instead use the space between
+    its inline-start <a>containing block</a> edge
+    and inline-end <a>static position</a>
+    or between its inline-start and inline-end <a>static positions</a>
+    by changing the <a>static-position containing block</a>’s
+    <a>content-distribution properties</a>.
+
 ### Multicol Containers ### {#distribution-multicol}
 
 	<table class="data align-details">
