[css-break-1][css-flexbox-1] Clarify that break propagation doesn't occur for out-of-flows, that it doesn't affect computed values, and that it uses order-modified document order. #2614

Author: fantasai

css-break-3/Overview.bs

@@ -256,15 +256,6 @@ Breaks Between Boxes: the 'break-before' and 'break-after' properties</h3>
     indicate that content should be kept together.
   </p>
 
-  <p>
-    Since breaks are only allowed between siblings,
-    not between a box and its container (see <a href="#possible-breaks">Possible Break Points</a>),
-    a 'break-before' value on a first-child box is propagated to its container.
-    Likewise a 'break-after' value on a last-child box is propagated to its container.
-    (Conflicting values <a href="#forced-breaks">combine</a> as defined below.)
-    This propagation stops before it breaks through the nearest matching fragmentation context.
-  </p>
-
   <p>
     Values for 'break-before' and 'break-after' are defined in the sub-sections below.
     User Agents must apply these properties to boxes in the normal flow of the <a>fragmentation root</a>.
@@ -365,6 +356,37 @@ Region Break Values</h4>
     </dd>
   </dl>
 
+<h4 id="break-propagation">
+Child→Parent Break Propagation</h4>
+
+  <p>
+    Since breaks are only allowed between siblings,
+    not between a box and its container
+    (see <a href="#possible-breaks">Possible Break Points</a>),
+    break values applied to children at the start/end of a parent
+    are <dfn lt="propagate|propagation">propagated</dfn> to the parent,
+    where they can take effect.
+  </p>
+
+  <p>
+    Specifically--
+    except in layout modes which define more specific rules
+    to account for reordering and parallel layout
+    (e.g. in <a href="http://www.w3.org/TR/css-flexbox-1/#pagination">flex layout</a> [[CSS-FLEXBOX-1]]
+    or <a href="http://www.w3.org/TR/css-grid-1/#pagination">grid layout</a> [[CSS-GRID-1]])--
+    a 'break-before' value on a first <a>in-flow</a> child box
+    is <a>propagated</a> to its container.
+    Likewise a 'break-after' value on a last <a>in-flow</a> child box
+    is <a>propagated</a> to its container.
+    (Conflicting values <a href="#forced-breaks">combine</a> as defined below.)
+    This propagation stops before it breaks through the nearest matching fragmentation context.
+  </p>
+
+  <p>
+    Break <a>propagation</a> does not affect <a>computed values</a>;
+    it is part of interpeting the elements’ computed values for layout.
+  </p>
+
 <h3 id="break-within">
 Breaks Within Boxes: the 'break-inside' property</h3>
 
@@ -527,7 +549,7 @@ Possible Break Points</h3>
 
   <p class="note">
     Other layout models may add breakpoints to the above classes.
-    For example, [[CSS3-FLEXBOX]] adds certain points within a flex formatting context
+    For example, [[CSS-FLEXBOX-1]] adds certain points within a flex formatting context
     to classes A and C.
   </p>
 
@@ -604,8 +626,8 @@ Forced Breaks</h3>
   <p>
     A <dfn export>forced break</dfn> is one explicitly indicated by the style sheet author.
     A <a>forced break</a> occurs at a <a href="#btw-blocks">class A break point</a> if,
-    among the 'break-after' properties specified on or propagated to the earlier sibling box
-    and the 'break-before' properties specified on or propagated to the later sibling box
+    among the 'break-after' properties specified on or <a>propagated</a> to the earlier sibling box
+    and the 'break-before' properties specified on or <a>propagated</a> to the later sibling box
     there is at least one with a <a>forced break value</a>.
     (Thus a <a>forced break value</a> effectively overrides any <a>avoid break value</a>
     that also applies at that break point.)
@@ -1102,6 +1124,17 @@ Transforms, Positioning, and Pagination</h3>
 <h2 class="no-num" id="changes">
 Changes</h2>
 
+  <p>The following significant changes were made since the
+    <a href="https://www.w3.org/TR/2017/CR-css-break-3-20170209/">8 February 2017 Candidate Recommendation</a>:
+  <ul>
+    <li>
+      Clarified that break propagation does not affect computed values
+      and that other layout modes (e.g. flex and grid) make adjustments
+      to the basic break propagation rules,
+      and corrected child-to-parent propagation to ignore <a>out-of-flow</a> children.
+      (<a href="https://github.com/w3c/csswg-drafts/issues/2614">Issue 2614</a>)
+  </ul>
+
   <p>The following significant changes were made since the
     <a href="https://www.w3.org/TR/2015/WD-css3-break-20150129/">29 January 2015 Working Draft</a>:
 

css-flexbox-1/Overview.bs

@@ -2976,33 +2976,40 @@ Fragmenting Flex Layout</h2>
 		The <a property lt="break-before">break-*</a> properties apply to flex containers as normal for block-level or inline-level boxes.
 		This section defines how they apply to flex items
 		and the contents of flex items.
+		See the <a href="http://www.w3.org/TR/css-break/">CSS Fragmentation Module</a>
+		for more context [[!CSS3-BREAK]].
 
 	<p>
 		The following breaking rules refer to the <a>fragmentation container</a> as the “page”.
 		The same rules apply in any other <a>fragmentation context</a>.
 		(Substitute “page” with the appropriate <a>fragmentation container</a> type as needed.)
-		See the CSS3 Fragmentation Module [[!CSS3-BREAK]].
 		For readability, in this section the terms "row" and "column" refer to the relative orientation
 		of the <a>flex container</a> with respect to the block flow direction of the <a>fragmentation context</a>,
 		rather than to that of the <a>flex container</a> itself.
 
 	<p>
-		The exact layout of a fragmented flex container is not defined in this level of Flexible Box Layout.
-		However, breaks inside a flex container are subject to the following rules:
+		The exact layout of a fragmented flex container
+		is not defined in this level of Flexible Box Layout.
+		However, breaks inside a flex container are subject to the following rules
+		(interpreted using <a>order-modified document order</a>):
 
 	<ul>
 		<li>
 			In a row flex container,
-			the 'break-before' and 'break-after' properties on flex items
+			the 'break-before' and 'break-after' values on flex items
 			are propagated to the flex line.
-			The 'break-before' property on the first line
-			and the 'break-after' property on the last line
+			The 'break-before' values on the first line
+			and the 'break-after' values on the last line
 			are propagated to the flex container.
 
+			Note: Break propagation
+			(like 'text-decoration' propagation)
+			does not affect <a>computed values</a>.
+
 		<li>
 			In a column flex container,
-			the 'break-before' property on the first item
-			and the 'break-after' property on the last item
+			the 'break-before' values on the first item
+			and the 'break-after' values on the last item
 			are propagated to the flex container.
 			Forced breaks on other items are applied to the item itself.
 
@@ -3582,6 +3589,36 @@ Changes since the 16 October 2017 CR</h3>
 			is floored by the table’s <a>min-content size</a>.
 			(<a href="https://github.com/w3c/csswg-drafts/issues/2442">Issue 2442</a>)
 
+		<li id="change-2017-break-propagation">
+			Clarified that break propagation does not affect computed values
+			and that <a>order-modified document order</a> is used.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/2614">Issue 2614</a>)
+			<blockquote>
+				<p>
+					The exact layout of a fragmented flex container
+					is not defined in this level of Flexible Box Layout.
+					However, breaks inside a flex container are subject to the following rules
+					<ins>(interpreted using <a>order-modified document order</a>)</ins>:
+
+				<ul>
+					<li>
+						In a row flex container,
+						the 'break-before' and 'break-after' values on flex items
+						are propagated to the flex line.
+						The 'break-before' values on the first line
+						and the 'break-after' values on the last line
+						are propagated to the flex container.
+
+						<ins>
+
+						Note: Break propagation
+						(like 'text-decoration' propagation)
+						does not affect <a>computed values</a>.
+
+						</ins>
+				</ul>
+			</blockquote>
+
 		<li>
 			Some minor editorial fixes and clarifications.
 	</ul>