[css-grid] Use leftover space instead of free space in description of <<flex>> since that is more accurate wrt terminology in the algorithm. w3c#1120

Author: fantasai

css-grid/Overview.bs

@@ -1692,23 +1692,23 @@ Flexible Lengths: the ''fr'' unit</h4>
 
 	A <dfn export>flexible length</dfn> or <dfn><<flex>></dfn> is a dimension
 	with the <dfn value for="<flex>" lt="fr|fr unit">fr</dfn> unit,
-	which represents a fraction of the <a>free space</a> in the <a>grid container</a>.
+	which represents a fraction of the <a>leftover space</a> in the <a>grid container</a>.
 
 	Note: <<flex>> values are not <<length>>s
 	(nor are they compatible with <<length>>s, like some <<percentage>> values),
 	so they cannot be represented in or combined with other unit types in ''calc()'' expressions.
 
-	The distribution of <a>free space</a> occurs after all non-flexible <a>track sizing functions</a> have reached their maximum.
-	The total size of such rows or columns is subtracted from the available space, yielding the <a>free space</a>,
+	The distribution of <a>leftover space</a> occurs after all non-flexible <a>track sizing functions</a> have reached their maximum.
+	The total size of such rows or columns is subtracted from the available space, yielding the <a>leftover space</a>,
 	which is then divided among the flex-sized rows and columns in proportion to their <a>flex factor</a>.
 
 	Note: Flexible lengths in a <a>track list</a> work similarly to flexible lengths with a zero base size in [[CSS-FLEXBOX-1]].
 
-	Each column or row's share of the <a>free space</a> can be computed as the column or row's
-	<code>&lt;flex> * &lt;free space> / &lt;sum of all <a>flex factors</a>&gt;</code>.
+	Each column or row's share of the <a>leftover space</a> can be computed as the column or row's
+	<code>&lt;flex> * &lt;leftover space> / &lt;sum of all <a>flex factors</a>&gt;</code>.
 
 	Note: If the sum of the <a>flex factors</a> is less than 1,
-	they'll take up only a corresponding fraction of the <a>free space</a>,
+	they'll take up only a corresponding fraction of the <a>leftover space</a>,
 	rather than expanding to fill the entire thing.
 	This is similar to how Flexbox [[CSS-FLEXBOX-1]] acts when the sum of the 'flex' values is less than 1.