[css-flexbox-1] Per WG resolution, make min-content cross size of multi-line column flexboxes act like it's a single column. w3c#6777

Author: tabatkins

css-flexbox-1/Overview.bs

@@ -3037,23 +3037,42 @@ Flex Container Intrinsic Cross Sizes</h4>
 	of its <a>flex items</a>.
 
 	For a <em><a>multi-line</a></em> <a>flex container</a>,
-	the <a>min-content</a>/<a>max-content</a> <a>cross size</a>
-	is the sum of the flex line cross sizes
-	resulting from sizing the flex container under a <a>cross-axis</a> <a>min-content constraint</a>/<a>max-content constraint</a> (respectively).
-	However, if the <a>flex container</a> is ''flex-flow: column wrap;'',
-	then it's sized by first finding the largest
-	<a lt="min-content contribution">min-content</a>/<a lt="min-content contribution">max-content</a>
-	<a>cross-size</a> contribution among the <a>flex items</a> (respectively),
-	then using that size as the <a>available space</a> in the <a>cross axis</a>
-	for each of the <a>flex items</a> during layout.
-
-	Note: This heuristic for ''column wrap'' <a>flex containers</a>
-	gives a reasonable approximation of the size that the <a>flex container</a> should be,
-	with each flex item ending up as min(<var>item’s own max-content</var>, <var>maximum min-content among all items</var>),
-	and each <a>flex line</a> no larger than its largest <a>flex item</a>.
-	It's not a <em>perfect</em> fit in some cases,
-	but doing it completely correct is insanely expensive,
-	and this works reasonably well.
+	the behavior depends on whether it's a row or column flexbox:
+
+	: ''flex-direction/row''  [=multi-line=] [=flex container=] [=cross-size=]
+	:: The <a>min-content</a>/<a>max-content</a> <a>cross size</a>
+		is the sum of the flex line cross sizes
+		resulting from sizing the flex container
+		under a <a>cross-axis</a> <a>min-content constraint</a>/<a>max-content constraint</a> (respectively).
+
+	: ''flex-direction/column'' [=multi-line=] [=flex container=] [=cross-size=]
+	:: The [=min-content=] [=cross size=]
+		is the largest [=min-content contribution=] among all of its [=flex items=].
+
+		Note: This heuristic effectively assumes a single flex line,
+		in order to guarantee that the [=min-content size=]
+		is smaller than the [=max-content size=].
+		If the flex container has a height constraint,
+		this will result in overflow,
+		but if the [=flex container=] is also a [=scroll container=],
+		it will at least be large enough to fit
+		any given column entirely within its [=scrollport=].
+
+		The [=max-content=] [=cross size=] is the sum of the [=flex line=] [=cross sizes=]
+		resulting from sizing the [=flex container=]
+		under a <a>cross-axis</a> <a>max-content constraint</a>,
+		using the largest <a lt="max-content contribution">max-content</a> <a>cross-size</a> contribution among the <a>flex items</a>
+		as the <a>available space</a> in the <a>cross axis</a>
+		for each of the <a>flex items</a> during layout.
+
+		Note: This heuristic gives a reasonable approximation
+		of the size that the <a>flex container</a> should be,
+		with each [=flex item=] laid out at its [=max-content contribution=] or larger,
+		and each <a>flex line</a> no larger than its largest <a>flex item</a>.
+		It's not a <em>perfect</em> fit in some cases,
+		but doing it completely correct is insanely expensive,
+		and this works reasonably well.
+
 
 <h4 id='intrinsic-item-contributions'>
 Flex Item Intrinsic Size Contributions</h4>