[css-text] Fix #277.

Author: fantasai

css-text/Overview.bs

@@ -690,7 +690,8 @@ Languages and Typesetting</h4>
       <li>If spaces or tabs at the end of a line are non-collapsible
          but have 'white-space' set to ''pre-wrap''
          the UA must either <a>hang</a> the <a>white space</a>
-         or visually collapse their character advance widths
+         or visually collapse the character advance widths
+         of any overflowing spaces
          such that they don't take up space in the line.
 
          Note: Hanging the white space rather than collapsing it