Clarify "Plain Unicode String"

Fixes #476

sections/editing.include

@@ -1609,9 +1609,9 @@
   </p>
 
   <h4 id="focus-processing-model">Clipboard actions and focus</h4>
-  
+
   <p>There are three clipboard actions that affect selection: cut, copy, and paste. Focus may follow selection, and user-agents handle this by default, but when custom clipboard actions are implemented the author needs to provide the following behaviors:</p>
-  
+
   <dl>
   <dt>Cut action:</dt>
   <dd>When a cut action is performed, the selected object should be removed and the collapsed section set in place of the cut object.</dd>
@@ -2240,7 +2240,7 @@
 
         <dt><i>Plain Unicode string</i></dt>
         <dd>
-        Text.
+        Text. Values must not be escaped.
         </dd>
 
         <dt><i>File</i></dt>