[css-grid] Better define 'free space'. Make grid sizing take the container's min/max-size into account.

Author: tabatkins

css-grid/Overview.bs

@@ -3179,7 +3179,7 @@ Grid Sizing Algorithm</h3>
 <h3 id='algo-terms'>
 Track Sizing Terminology</h3>
 
-	<dl>
+	<dl noexport>
 		<dt><dfn>min track sizing function</dfn>
 		<dd>
 			If the track was sized with a ''minmax()'' function,
@@ -3192,14 +3192,21 @@ Track Sizing Terminology</h3>
 			this is the second argument to that function.
 			Otherwise, it's the track's sizing function.
 
-		<dt><dfn>free space</dfn>
+		<dt><dfn>available grid space</dfn>
 		<dd>
-			Equal to the <a>available space</a> minus the sum of the <a>base sizes</a> of all the grid tracks,
-			clamped to a minimum of zero.
-			This value can change over the course of the algorithm,
-			as <a>base sizes</a> are adjusted.
+			Independently in each dimension, the <a>available grid space</a> is:
+
+			* If the <a>grid container's</a> size is definite, then use the size of the resulting content box.
+			* If the <a>grid container</a> is being sized under a <a>min-content constraint</a> or <a>max-content constraint</a>  , then the <a>available grid space</a> is that constraint (and is indefinite).
+
+			Note: ''auto'' sizes that indicate content-based sizing (e.g. the height of a block-level box in horizontal writing modes) are equivalent to ''max-content''.
+
+			In all cases, clamp the <a>available grid space</a> by the <a>grid container's</a> min/max-width/height properties, if they are definite.
 
-			If <a>available space</a> is <a>indefinite</a>,
+		<dt><dfn>free space</dfn>
+		<dd>
+			Equal to the <a>available grid space</a> minus the sum of the <a>base sizes</a> of all the grid tracks, floored at zero.
+			If <a>available grid space</a> is <a>indefinite</a>,
 			the <a>free space</a> is <a>indefinite</a> as well.
 
 		<dt><dfn>span count</dfn>
@@ -3501,6 +3508,11 @@ Maximize Tracks</h3>
 	if sizing under a <a>min-content constraint</a>,
 	the <a>free space</a> is zero.
 
+	If this would cause the grid to be larger than the <a>grid container's</a> <a property lt=max-width>max-width/height</a>,
+	then redo this step,
+	treating the <a>available grid space</a> as equal to the <a>grid container's</a> content box size
+	when it's sized to its <a property lt=max-width>max-width/height</a>.
+
 <h3 id="algo-flex-tracks">
 Stretch Flexible Tracks</h3>
 
@@ -3509,6 +3521,7 @@ Stretch Flexible Tracks</h3>
 	without exceeding the <a>available space</a>.
 
 	First, find the used <a>flex fraction</a>:
+
 	<dl>
 		<dt>If the <a>free space</a> is zero:
 		<dd>
@@ -3519,7 +3532,7 @@ Stretch Flexible Tracks</h3>
 			The used <a>flex fraction</a> is the result of
 			<a href="#algo-find-fr-size">finding the size of an fr</a>
 			using all of the <a>grid tracks</a>
-			and a <a>space to fill</a> of the <a>available space</a>.
+			and a <a>space to fill</a> of the <a>available grid space</a>.
 
 		<dt>If the <a>free space</a> is an <a>indefinite</a> length:
 		<dd>
@@ -3535,6 +3548,12 @@ Stretch Flexible Tracks</h3>
 					using all the grid tracks that the item crosses
 					and a <a>space to fill</a> of the item's <a>max-content contribution</a>.
 			</ul>
+
+			If using this <a>flex fraction</a> would cause the <a>grid</a> to be smaller than the <a>grid container's</a> <a property lt=min-width>min-width/height</a>
+			(or larger than the <a>grid container's</a> <a property lt=max-width>max-width/height</a>),
+			then redo this step,
+			treating the <a>free space</a> as definite
+			and the <a>available grid space</a> as equal to the <a>grid container's</a> content box size when it's sized to its <a property lt=min-width>min-width/height</a> (<a property lt=max-width>max-width/height</a>).
 	</dl>
 
 	For each flexible track,