clearify pipe character (|).

Author: mumumu

appendices/migration85/incompatible.xml

@@ -369,8 +369,8 @@
 
   <para>
    Attempting to write session data where <varname>$_SESSION</varname> has a key
-   containing the pipe character will now emit a warning instead of silently
-   failing.
+   containing the pipe character (<literal>|</literal>) will now emit a warning
+   instead of silently failing.
   </para>
 
  </sect2>