[css-flexbox-1] Mark intrinsic sizing algorithm as having Web-compat issues. #8884

Author: fantasai

css-flexbox-1/Overview.bs

@@ -2878,15 +2878,32 @@ Intrinsic Sizes</h3>
 Flex Container Intrinsic Main Sizes</h4>
 
 	The <strong><a>max-content</a> <a>main size</a> of a <a>flex container</a></strong>
-	is, fundamentally, the smallest size the <a>flex container</a> can take
+	is, theoretically, the smallest size the <a>flex container</a> can take
 	such that when flex layout is run with that container size,
 	each [=flex item=] ends up at least as large as
 	its [[#intrinsic-item-contributions|max-content contribution]],
 	to the extent allowed by the items’ flexibility.
 
-	It is calculated,
-	considering only non-[=collapsed=] [=flex items=],
-	by:
+	The <strong>[=min-content=] [=main size=] is, theoretically,
+	the smallest size the [=flex container can take=]
+	such that no items overflow it,
+	and no item's contents overflow the item--
+	setting aside the cases in which the boxes layouts are <em>defined</em> to overflow
+	(for example with negative margins or percentage sizes that add up to more than 100%).
+
+<h5 id='intrinsic-main-sizes-ideal'>
+Ideal Algorithm</h5>
+
+	Note: The following algorithm calculates the [=flex container=]’s ideal
+	intrinsic [=main sizes=].
+	However, because it was not implemented correctly initially,
+	and existing content became dependent on the (unfortunately consistent) incorrect implemented behavior,
+	<a href="https://github.com/w3c/csswg-drafts/issues/8884">it is not Web-compatible</a>.
+	Implementers and the CSS Working Group are investigating to what extent
+	Web browser implementations can safely approach this behavior,
+	and further experimentation is welcome.
+
+	Considering only non-[=collapsed=] [=flex items=];
 
 	<ol>
 		<li>
@@ -2940,15 +2957,6 @@ Flex Container Intrinsic Main Sizes</h4>
 	except that the <a>flex items</a>’ [[#intrinsic-item-contributions|min-content contributions]] are used
 	instead of their [[#intrinsic-item-contributions|max-content contributions]].
 
-	However, for a <em><a>multi-line</a></em> container,
-	the [=min-content=] [=main size=] is simply the largest [[#intrinsic-item-contributions|min-content contribution]]
-	of all the non-[=collapsed=] <a>flex items</a> in the <a>flex container</a>.
-	For this purpose,
-	each item's contribution
-	is capped by the item’s [=flex base size=] if the item is not growable,
-	floored by the item’s [=flex base size=] if the item is not shrinkable,
-	and then further clamped by the item's min and max main sizes.
-
 	<details class=note>
 		<summary>Implications of this algorithm when the sum of flex is less than 1</summary>
 
@@ -3029,6 +3037,27 @@ Flex Container Intrinsic Main Sizes</h4>
 		</details>
 	</details>
 
+<h5 id="intrinsic-main-sizes-compat">
+Web-compatible Intrinsic Sizing Algorithm</h5>
+
+	Note: The following algorithm has been demonstrated to be Web-compatible.
+	It may be altered in the future to bring it closer to the ideal algorithm above,
+	if possible.
+
+	ISSUE(8884): Outline Web-compatible algorithm here, once we have one.
+
+<h5 id="intrinsic-main-sizes-multiline">
+Multi-line Min-content Algorithm</h5>
+
+	For a <em><a>multi-line</a></em> container,
+	the [=min-content=] [=main size=] is simply the largest [[#intrinsic-item-contributions|min-content contribution]]
+	of all the non-[=collapsed=] <a>flex items</a> in the <a>flex container</a>.
+	For this purpose,
+	each item's contribution
+	is capped by the item’s [=flex base size=] if the item is not growable,
+	floored by the item’s [=flex base size=] if the item is not shrinkable,
+	and then further clamped by the item's min and max main sizes.
+
 <h4 id='intrinsic-cross-sizes'>
 Flex Container Intrinsic Cross Sizes</h4>