--- modules/node/node.pages.inc	2010-11-26 20:23:01.000000000 +0100
+++ modules/node/node.pages.inc	2010-12-18 15:39:53.000000000 +0100
@@ -387,7 +387,7 @@ function theme_node_preview($variables) 
 
   // Do we need to preview trimmed version of post as well as full version?
   if ($trimmed != $full) {
-    drupal_set_message(t('The trimmed version of your post shows what your post looks like when promoted to the main page or when exported for syndication.<span class="no-js"> You can insert the delimiter "&lt;!--break--&gt;" (without the quotes) to fine-tune where your post gets split.</span>'));
+    drupal_set_message(t('The trimmed version of your post shows what your post looks like when promoted to the main page or when exported for syndication.<span class="no-js"> For content types that display a "Long text and summary" field (such as Body), you can insert the delimiter "&lt;!--break--&gt;" (without the quotes) to fine-tune where your post gets split.</span>'));
     $output .= '<h3>' . t('Preview trimmed version') . '</h3>';
     $output .= $trimmed;
     $output .= '<h3>' . t('Preview full version') . '</h3>';