[css-flexbox-1] Make space-* fallback to safe alignment w3c#10154

Author: fantasai

css-flexbox-1/Overview.bs

@@ -1980,7 +1980,7 @@ Axis Alignment: the 'justify-content' property</h3>
 			<a>Flex items</a> are evenly distributed in the line.
 			If the leftover free-space is negative
 			or there is only a single <a>flex item</a> on the line,
-			this value is identical to <a value for=justify-content>flex-start</a>.
+			this value falls back to <a value for=justify-content>safe flex-start</a>.
 			Otherwise,
 			the <a>main-start</a> margin edge of the first <a>flex item</a> on the line
 			is placed flush with the <a>main-start</a> edge of the line,
@@ -1995,7 +1995,7 @@ Axis Alignment: the 'justify-content' property</h3>
 			with half-size spaces on either end.
 			If the leftover free-space is negative or
 			there is only a single <a>flex item</a> on the line,
-			this value is identical to <a value for=justify-content>center</a>.
+			this value falls back to <a value for=justify-content>safe center</a>.
 			Otherwise, the <a>flex items</a> on the line are distributed
 			such that the spacing between any two adjacent <a>flex items</a> on the line is the same,
 			and the spacing between the first/last <a>flex items</a> and the <a>flex container</a> edges
@@ -2209,7 +2209,7 @@ Packing Flex Lines: the 'align-content' property</h3>
 			Lines are evenly distributed in the flex container.
 			If the leftover free-space is negative
 			or there is only a single <a>flex line</a> in the flex container,
-			this value is identical to <a value for=align-content>flex-start</a>.
+			this value falls back to <a value for=align-content>safe flex-start</a>.
 			Otherwise,
 			the <a>cross-start</a> edge of the first line in the flex container
 			is placed flush with the <a>cross-start</a> content edge of the flex container,
@@ -2223,7 +2223,7 @@ Packing Flex Lines: the 'align-content' property</h3>
 			Lines are evenly distributed in the flex container,
 			with half-size spaces on either end.
 			If the leftover free-space is negative
-			this value is identical to <a value for=align-content>center</a>.
+			this value falls back to <a value for=align-content>safe center</a>.
 			Otherwise, the lines in the flex container are distributed
 			such that the spacing between any two adjacent lines is the same,
 			and the spacing between the first/last lines and the <a>flex container</a> edges
@@ -2233,7 +2233,7 @@ Packing Flex Lines: the 'align-content' property</h3>
 		<dd>
 			Lines stretch to take up the remaining space.
 			If the leftover free-space is negative,
-			this value is identical to <a value for=align-content>flex-start</a>.
+			this value falls back to <a value for=align-content>safe flex-start</a>.
 			Otherwise,
 			the free-space is split equally between all of the lines,
 			increasing their cross size.
@@ -3842,6 +3842,11 @@ Changes since the <a href="https://www.w3.org/TR/2018/CR-css-flexbox-1-20181119/
 				and thus the provisions in [[css-sizing-3#intrinsic-contribution]] apply.
 			</blockquote>
 
+		<li id="change-2018-safe-fallback">
+			Made the fallback alignment (in case of negative free space)
+			for the ''space-*'' keywords apply ''overflow-position/safe''.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/10154">Issue 10154</a>)
+
 		<li id="change-2018-content-based-editorial">
 			Redrafted the definition of [=content-based minimum size=]
 			for easier reading. (Editorial)