[css-grid] Make grid items maintain intrinsic ratio in default case per #523. (First cut, needs review, didn't address object-fit question.)

Author: fantasai

css-grid/Overview.bs

@@ -1063,17 +1063,55 @@ Grid Items</h2>
 <h3 id="grid-item-sizing">
 	Grid Item Sizing</h3>
 
-	A <a>grid item</a> is sized within the containing block defined by its <a>grid area</a>
-	using the 'width' calculation rules for non-replaced block boxes
-	as defined in <a href="https://www.w3.org/TR/CSS21/visudet.html#blockwidth">CSS2.1 &sect; 10.3.3</a>
-	(meaning ''width/auto'' values in either axis are
-	effectively sized to fill the remaining space).
+	A <a>grid item</a> is sized within the containing block defined by its <a>grid area</a>.
+
+	Items without an intrinsic ratio use, in both axes,
+	the 'width' calculation rules for non-replaced block boxes
+	as defined in <a href="https://www.w3.org/TR/CSS21/visudet.html#blockwidth">CSS2.1 &sect; 10.3.3</a>.
+	(Meaning, ''width/auto'' values in either axis are
+	effectively sized to fill the remaining space.)
 	However, the <a>box alignment properties</a> have special effects:
 	when 'align-self'/'justify-self' is neither ''justify-self/normal'' nor ''justify-self/stretch'',
 	an ''width/auto'' size for the <a>grid item</a> in that axis
 	is treated as ''width/fit-content'' instead of as the <a>fill-available size</a>.
 	See [[#alignment]].
 
+	Items with an intrinsic ratio follow the same rules,
+	except that in the case of a ''align-self/normal'' alignment value,
+	an ''width/auto'' size for the <a>grid item</a>
+	is further reduced or increased in that axis
+	(while maintaining any specified minimum or maximum size)
+	if necessary to maintain the intrinsic aspect ratio.
+	If both axes have ''align-self/normal'' alignment and ''width/auto'' sizing,
+	then this adjustment is made in the axis that needs reduction.
+
+	<div class="note">
+		The following informative table summarizes the automatic sizing of grid items:
+
+		<table class=data>
+			<caption>Summary of automatic sizing behavior of grid items</caption>
+			<thead>
+				<tr>
+					<th>Alignment
+					<th>Non-replaced Element Size
+					<th>Replaced Element Size
+			<tbody>
+				<tr>
+					<th scope=row>''align-self/normal''
+					<td>Fill grid area
+					<td>''object-fit/contain''-type sizing into grid area
+				<tr>
+					<th scope=row>''align-self/stretch''
+					<td>Fill grid area
+					<td>Fill grid area
+				<tr>
+					<th scope=row>''align-self/start''/''align-self/center''/etc.
+					<td>''width/fit-content'' sizing (like floats)
+					<td>Use intrinsic size
+		</table>
+	</div>
+
+
 	Note: The ''min-width/auto'' value of 'min-width' and 'min-height'
 	affects track sizing in the relevant axis
 	similar to how it affects the main size of a <a>flex item</a>.
@@ -4268,35 +4306,15 @@ Acknowledgements</h2>
 <h2 class="no-num" id="changes">
 Changes</h2>
 
-	Changes since the <a href="https://www.w3.org/TR/2016/WD-css-grid-1-20160519/">19 May 2016 Working Draft</a> are:
-
+	Changes since the <a href="https://www.w3.org/TR/2016/CR-css-grid-1-20160929/">29 September 2016 Candidate Recommendation</a> are:
 	<ul>
-		<li>Disallowed ''repeat()'' syntax in 'grid-template' shorthand syntax--
-			since this is somewhat incompatible with the ASCII-art design of the syntax, and was never intended to be allowed.
-			(<a href="https://drafts.csswg.org/css-grid-1/issues-wd-20160519#issue-3">Issue 3</a>)
-		<li>Clamped <a>automatic minimum size</a> of grid items inside tracks with <a>fixed sizing functions</a>.
-			(<a href="https://drafts.csswg.org/css-grid-1/issues-wd-20160519#issue-15">Issue 15</a>)
-		<li>Fixed handling of ''fit-content()'' in the track sizing algorithm.
-			(<a href="https://drafts.csswg.org/css-grid-1/issues-wd-20160519#issue-13">Issue 13</a>)
-		<li>Allowed UAs to (optionally) back-compute percentage track sizes.
-			(<a href="https://drafts.csswg.org/css-grid-1/issues-wd-20160519#issue-26">Issue 26</a>)
-		<li>Correctly and completely defined ''auto''-sizing of grid items.
-			(<a href="https://drafts.csswg.org/css-grid-1/issues-wd-20160519#issue-21">Issue 21</a>)
-		<li>Made the handling of <a>collapsed tracks</a> more explicit.
-			(<a href="https://drafts.csswg.org/css-grid-1/issues-wd-20160519#issue-8">Issue 8</a>)
-		<li>Fixed grammar error in definition of <<auto-track-list>>.
-			(<a href="https://drafts.csswg.org/css-grid-1/issues-wd-20160519#issue-1">Issue 1</a>)
-		<li>Fixed some tangled up text about how subgrids receive line names from their parent grid.
-		<li>Clarified that percentage gutters are calculated exactly like empty percentage tracks.
-			(<a href="https://drafts.csswg.org/css-grid-1/issues-wd-20160519#issue-20">Issue 20</a>)
-		<li>Made missing baselines synthesize from the border box.
-			(<a href="https://drafts.csswg.org/css-grid-1/issues-wd-20160519#issue-22">Issue 22</a>)
-		<li>Miscellaneous minor clarifications.
+		<li>Applied flex factor clamping to 1 also to indefinite case.
+			(See <a href="https://lists.w3.org/Archives/Public/www-style/2015Sep/0032.html">discussion</a>.)
+		<li>Fixed automatic sizing of grid items with an intrinsic ratio
+			so that they maintain their intrinsic ratio
+			whenever the alignment properties are ''align-self/normal'' (the default case).
 	</ul>
 
-	A <a href="https://drafts.csswg.org/css-grid-1/issues-wd-20160519">Disposition of Comments</a> is available.
-	See also <a href="https://www.w3.org/TR/2016/WD-css-grid-1-20160519/#changes">previous changes</a>.
-
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