[css-grid-1][css-flexbox-1] Per #4065, rephrase the grid/flex blockification rules in terms of explicit 'display' values rather than box-tree results.

Author: tabatkins

css-flexbox-1/Overview.bs

@@ -674,13 +674,18 @@ Flex Items</h2>
 	Note: Authors reading this spec may want to
 	<a href="#item-margins">skip past the following box-generation and static position details</a>.
 
-	The 'display' value of a <a>flex item</a> is <a>blockified</a>:
-	if the specified 'display' of an in-flow child of an element generating a <a>flex container</a>
-	is an inline-level value, it computes to its block-level equivalent.
+	If the [=computed value|computed=] 'display' value of an element's nearest ancestor element
+	(skipping ''display:contents'' ancestors)
+	is ''flex'' or ''inline-flex'',
+	the element's own 'display' value is [=blockified=].
 	(See <a href="https://www.w3.org/TR/CSS2/visuren.html#dis-pos-flo">CSS2.1&sect;9.7</a> [[!CSS21]]
-	and <a href="https://www.w3.org/TR/css-display/#transformations">CSS Display</a> [[!CSS3-DISPLAY]]
+	and [[css-display-3#transformations]]
 	for details on this type of 'display' value conversion.)
 
+	Note: Blockification still occurs even when the ''flex'' or ''inline-flex'' element does not end up generating a [=flex container=] box,
+	e.g. when it is [=replaced element|replaced=]
+	or in a ''display: none'' subtree.
+
 	Note: Some values of 'display' normally trigger the creation of anonymous boxes around the original box.
 	If such a box is a <a>flex item</a>,
 	it is blockified first,

css-grid-1/Overview.bs

@@ -1061,13 +1061,18 @@ Grid Items</h2>
 	they participate in their container's <a>grid formatting context</a>,
 	not in a block formatting context.
 
-	The 'display' value of a <a>grid item</a> is <a>blockified</a>:
-	if the specified 'display' of an in-flow child of an element generating a <a>grid container</a>
-	is an inline-level value, it computes to its block-level equivalent.
+	If the [=computed value|computed=] 'display' value of an element's nearest ancestor element
+	(skipping ''display:contents'' ancestors)
+	is ''grid'' or ''inline-grid'',
+	the element's own 'display' value is [=blockified=].
 	(See <a href="https://www.w3.org/TR/CSS2/visuren.html#dis-pos-flo">CSS2.1&sect;9.7</a> [[!CSS21]]
-	and <a href="https://www.w3.org/TR/css-display/#transformations">CSS Display</a> [[!CSS3-DISPLAY]]
+	and [[css-display-3#transformations]]
 	for details on this type of 'display' value conversion.)
 
+	Note: Blockification still occurs even when the ''grid'' or ''inline-grid'' element does not end up generating a [=grid container=] box,
+	e.g. when it is [=replaced element|replaced=]
+	or in a ''display: none'' subtree.
+
 	Note: Some values of 'display' normally trigger the creation of anonymous boxes around the original box.
 	If such a box is a <a>grid item</a>,
 	it is blockified first,
@@ -1899,7 +1904,7 @@ Resolved Value of a Track Listing</h4>
 	The 'grid-template-rows' and 'grid-template-columns' properties are
 	<a>resolved value special case properties</a>. [[!CSSOM]]
 
-	When an element generates a [=grid container box=],
+	When an element generates a [=grid container=] box,
 	the <a href="https://www.w3.org/TR/cssom/#resolved-values">resolved value</a>
 	of the 'grid-template-rows' and 'grid-template-columns' properties is the <a>used value</a>,
 	serialized with: