[css-text-4] Better definition of what's allowed for preserve-auto.

Author: fantasai

css-text-4/Overview.bs

@@ -73,7 +73,8 @@ White Space Collapsing: the 'text-space-collapse' property</h3>
 			the UA <em>may</em> visually collapse
 			the advance widths of preserved white space
 			that occurs at the end of a line,
-			and is not required to honor soft wrap opportunities between such spaces.
+			<em>or</em> treat them as collapsed for the purpose of wrapping text
+			(such that the white space overflows the line instead of wrapping to the front of the next line).
 
 		<dt><dfn>preserve-trim</dfn>
 		<dd>