[css-inline-3] Shift linebox-relative alignment values to baseline-shift per #5180

Author: fantasai

css-inline-3/Overview.bs

@@ -227,15 +227,15 @@ Layout Within Line Boxes</h3>
 				Issue(5178): Handle negative half-leading?
 		</ul>
 
-	2. The [=inline-level boxes=] with [=baseline alignment values=]
+	2. The [=inline-level boxes=]
 		are aligned in the [=block axis=]
 		according to 'dominant-baseline' and 'vertical-align'.
+		Those with [=line-relative values=] for 'baseline-shift'
+		are assumed to be aligned so as to minimize the line box height.
 
 	3. The [=line box=]’s [=logical height=] is calculated
 		to exactly include the aligned [=layout bounds=]
 		of all its [=inline-level boxes=].
-		Those with [=line-relative alignment values=]
-		are assumed to be aligned so as to minimize the line box height.
 
 	4. The [=root inline box=]’s [=aligned subtree=]
 		and boxes with line-box&ndash;relative 'vertical-align' values
@@ -662,6 +662,15 @@ Transverse Box Alignment: the 'vertical-align' property</h3>
 		unless specifically needing to cascade its longhands independently
 		or (on SVG elements) to support legacy SVG implementations.
 
+	Note: 'vertical-align' can also affect the alignment of table cells
+	when 'align-content' is ''align-content/normal''.
+	Specifically, ''vertical-align/top'' (''baseline-shift: top'') maps it to ''align-content/start'',
+	''vertical-align/bottom'' (''baseline-shift: bottom'')  to ''align-content/end'',
+	and ''vertical-align/center'' (''alignment-baseline: middle'') to ''align-content/center''.
+	See [[css-align-3#distribution-block]].
+
+	ISSUE(https://github.com/w3c/csswg-drafts/issues/5234): Define mapping of ''alignment-baseline: middle; baseline-shift: top''.
+
 <h4 id="baseline-source">
 Alignment Baseline Source: the 'baseline-source' longhand</h4>
 
@@ -715,11 +724,7 @@ Alignment Baseline Type: the 'alignment-baseline' longhand</h4>
 	prior to applying its [=post-alignment shift=]
 	(if applicable).
 
-<h5 class="no-toc" id="alignment-baseline-baselines">
-Baseline Alignment Values</h5>
-
-	The <dfn>baseline alignment values</dfn>
-	are defined as follows:
+	Values are defined as follows:
 
 	<dl dfn-for=alignment-baseline dfn-type=value>
 		<dt><dfn>baseline</dfn>
@@ -772,43 +777,6 @@ Baseline Alignment Values</h5>
 	these values instead specify the [=baseline=] that is aligned
 	to the SVG <a>current text position</a>.
 
-<h5 class="no-toc" id="alignment-baseline-linebox">
-Line-Relative Alignment Values</h5>
-
-	The <dfn>line-relative alignment values</dfn>,
-	which reference the [=line-over=] and [=line-under=] edges
-	of the box’s [=aligned subtree=]
-	and align with respect to the corresponding edges of the [=line box=] itself,
-	are defined below:
-
-	<dl dfn-for=alignment-baseline dfn-type=value>
-		<dt><dfn>top</dfn>
-		<dd>
-			Align the [=line-over=] edge of the [=aligned subtree=]
-			with the [=line-over=] edge of the [=line box=].
-
-		<dt><dfn>center</dfn>
-		<dd>
-			Align the center of the [=aligned subtree=]
-			with the center of the [=line box=].
-
-		<dt><dfn>bottom</dfn>
-		<dd>
-			Align the [=line-under=] edge of the [=aligned subtree=]
-			with the [=line-under=] edge of the [=line box=].
-	</dl>
-
-	Since the block-axis bounds of an [=inline box=]
-	do not as a rule encompass their contents,
-	these values use the bounds of the [=aligned subtree=].
-	The <dfn>aligned subtree</dfn> of an [=inline box=] contains that box
-	and the [=aligned subtrees=] of all children [=inline boxes=]
-	whose computed 'alignment-baseline' value
-	is not itself a [=line-relative alignment value=].
-	The [=line-over=] edge of the [=aligned subtree=]
-	is the highest [=over=] edge of the boxes in the subtree,
-	and the [=line-under=] edge is analogously the lowest.
-
 <h5 class="no-toc" id="alignment-baseline-svg-legacy">
 Legacy Values for SVG</h5>
 
@@ -825,18 +793,22 @@ Post-Alignment Shift: the 'baseline-shift' longhand</h4>
 
 	<pre class="propdef">
 	Name: baseline-shift
-	Value: <<length-percentage>> | sub | super
+	Value: <<length-percentage>> | sub | super | top | center | bottom
 	Initial: 0
 	Applies to: inline-level boxes and SVG <a>text content elements</a>
-	<!-- table cells left out b/c CSS2.1 vertical-align values must have no effect... -->
 	Inherited: no
 	Percentages: refer to the used value of 'line-height'
 	Computed value: the specified keyword and/or a computed <<length-percentage>> value
 	</pre>
 
-	This property specifies the box’s <dfn>post-alignment shift</dfn>:
-	by how much the box is shifted up from its aligned position.
-	It does not apply when 'alignment-baseline' is ''alignment-baseline/top'' or ''alignment-baseline/bottom''.
+	This property specifies the box’s <dfn>post-alignment shift</dfn>.
+	The <dfn>baseline-relative values</dfn>
+	<<length-percentage>>, ''baseline-shift/sub'', ''baseline-shift/super''
+	shift the box relative to its baseline-aligned position,
+	whereas the <dfn>line-relative values</dfn>
+	''baseline-shift/top'', ''baseline-shift/center'', and ''baseline-shift/bottom''
+	shift the [=inline box=] and its contents
+	relative to the bounds of its [=line box=].
 
 	<p class="advisement">
 		Authors should use the 'vertical-align' shorthand,
@@ -861,11 +833,38 @@ Post-Alignment Shift: the 'baseline-shift' longhand</h4>
 		<dt><dfn>super</dfn>
 		<dd>Raise by the offset appropriate for superscripts of the parent’s box.
 		(The UA should use the parent’s font data to find this offset whenever possible.)
+
+		<dt><dfn>top</dfn>
+		<dd>
+			Align the [=line-over=] edge of the [=aligned subtree=]
+			with the [=line-over=] edge of the [=line box=].
+
+		<dt><dfn>center</dfn>
+		<dd>
+			Align the center of the [=aligned subtree=]
+			with the center of the [=line box=].
+
+		<dt><dfn>bottom</dfn>
+		<dd>
+			Align the [=line-under=] edge of the [=aligned subtree=]
+			with the [=line-under=] edge of the [=line box=].
 	</dl>
 
-	<p>User agents <em>may</em> additionally support the keyword <dfn value for=baseline-shift>baseline</dfn>
-	as computing to ''0''
+	The <dfn>aligned subtree</dfn> of an [=inline box=] contains that box
+	and the [=aligned subtrees=] of all children [=inline boxes=]
+	whose computed 'alignment-baseline' value
+	is not itself a [=line-relative value=].
+	The [=line-over=] edge of the [=aligned subtree=]
+	is the highest [=over=] edge of the boxes in the subtree,
+	and the [=line-under=] edge is analogously the lowest.
+
+<h5 class="no-toc" id="baseline-shift-svg-legacy">
+Legacy Values for SVG</h5>
+
+	<p>User agents <em>may</em> additionally support
+	the keyword <dfn value for=baseline-shift>baseline</dfn> as computing to ''0''
 	if is necessary for them to support legacy SVG content.
+	This value is not allowed in the 'vertical-align' shorthand.
 
 	Issue: We would prefer to remove the ''baseline-shift/baseline'' value, and are looking for feedback from SVG user agents as to whether it's necessary.