[css-grid-1] Clarify what we're fixing the row/column sizes for (figu…

…ring out available space). Also wordsmith. #3046.

css-grid-1/Overview.bs

@@ -3608,18 +3608,28 @@ Grid Sizing Algorithm</h3>
 		</div>
 
 		<li>
-			Next, the <a>track sizing algorithm</a> resolves the sizes of the <a>grid rows</a>,
-			using the <a>grid column</a> sizes calculated in the previous step
-			and the effective column gap sizes after applying 'justify-content'.
+			Next, the <a>track sizing algorithm</a> resolves the sizes of the <a>grid rows</a>.
+
+			To find the <a>inline-axis</a> <a>available space</a>
+			for any items whose <a>block-axis</a> size contributions require it,
+			use the <a>grid column</a> sizes calculated in the previous step.
+			If the <a>grid container</a>’s <a>inline size</a> is <a>definite</a>,
+			also apply 'justify-content'
+			to account for the effective column gap sizes.
 
 		<li>
 			Then, if the <a>min-content contribution</a> of any grid item has changed
 			based on the row sizes and alignment calculated in step 2,
 			re-resolve the sizes of the <a>grid columns</a>
 			with the new <a lt="min-content contribution">min-content</a>
-			and <a>max-content contributions</a> (once only),
-			using the <a>grid row</a> sizes calculated in the previous step
-			along with the effective row gap sizes calculated by applying 'align-content'.
+			and <a>max-content contributions</a> (once only).
+
+			To find the <a>block-axis</a> <a>available space</a>
+			for any items whose <a>inline-axis</a> size contributions require it,
+			use the <a>grid row</a> sizes calculated in the previous step.
+			If the <a>grid container</a>’s <a>block size</a> is <a>definite</a>,
+			also apply 'align-content'
+			to account for the effective row gap sizes.
 
 			<div class="note">
 				This repetition is necessary for cases where the <a>inline size</a> of a <a>grid item</a>
@@ -3634,9 +3644,14 @@ Grid Sizing Algorithm</h3>
 			based on the column sizes and alignment calculated in step 3,
 			re-resolve the sizes of the <a>grid rows</a>
 			with the new <a lt="min-content contribution">min-content</a>
-			and <a>max-content contributions</a> (once only),
-			using the <a>grid column</a> sizes calculated in the previous step
-			along with the effective column gap sizes calculated by applying 'justify-content'.
+			and <a>max-content contributions</a> (once only).
+
+			To find the <a>inline-axis</a> <a>available space</a>
+			for any items whose <a>block-axis</a> size contributions require it,
+			use the <a>grid column</a> sizes calculated in the previous step.
+			If the <a>grid container</a>’s <a>inline size</a> is <a>definite</a>,
+			also apply 'justify-content'
+			to account for the effective column gap sizes.
 
 		<li>
 			Finally, the <a>grid container</a> is sized