Index: node.module
===================================================================
--- node.module	(revision 97)
+++ node.module	(working copy)
@@ -188,10 +188,10 @@
   foreach ($breakpoints as $point => $charnum) {
     if ($length = strpos($body, $point, $size)) {
-      return substr($body, 0, $length + $charnum);
+      return _node_htmlcorrector_process(substr($body, 0, $length + $charnum));
     }
   }
 
   // If all else fails, we simply truncate the string.
-  return truncate_utf8($body, $size);
+  return _node_htmlcorrector_process(truncate_utf8($body, $size));
 }
 
@@ -2470,3 +2470,72 @@
  */
 
+/*
+ * Utility for ensuring closed tags in auto-generated teasers
+ *
+ */
+
+function _node_htmlcorrector_process($text) {
+  // Tags which cannot be nested but are typically left unclosed.
+  $nonesting = array('li', 'p');
+  
+  // Single use tags in HTML4
+  $singleuse = array('base', 'meta', 'link', 'hr', 'br', 'param', 'img', 'area', 'input', 'col', 'frame');
+
+  // Properly entify angles
+  $text = preg_replace('!<([^a-zA-Z/])!', '&lt;\1', $text);
 
+  // Splits tags from text
+  $split = preg_split('/<([^>]+?)>/', $text, -1, PREG_SPLIT_DELIM_CAPTURE);
+  // Note: PHP ensures the array consists of alternating delimiters and literals
+  // and begins and ends with a literal (inserting $null as required).
+
+  $tag = false; // Odd/even counter. Tag or no tag.
+  $stack = array();
+  $output = '';
+  foreach ($split as $value) {
+    // HTML tag
+    if ($tag) {
+      list($tagname) = explode(' ', strtolower($value), 2);
+      // Closing tag
+      if ($tagname{0} == '/') {
+        $tagname = substr($tagname, 1);
+        if (!in_array($tagname, $singleuse)) {
+          // See if we have other tags lingering first, and close them
+          while (($stack[0] != $tagname) && count($stack)) {
+            $output .= '</'. array_shift($stack) .'>';
+          }
+          // If the tag was not found, just leave it out;
+          if (count($stack)) {
+            $output .= '</'. array_shift($stack) .'>';
+          }
+        }
+      }
+      // Opening tag
+      else {
+        // See if we have an identical tag already open and close it if desired.
+        if (count($stack) && ($stack[0] == $tagname) && in_array($stack[0], $nonesting)) {
+          $output .= '</'. array_shift($stack) .'>';
+        }
+        // Push non-single-use tags onto the stack
+        if (!in_array($tagname, $singleuse)) {
+          array_unshift($stack, $tagname);
+        }
+        // Add trailing slash to single-use tags as per X(HT)ML.
+        else {
+          $value = rtrim($value, ' /') . ' /';
+        }
+        $output .= '<'. $value .'>';
+      }
+    }
+    else {
+      // Passthrough
+      $output .= $value;
+    }
+    $tag = !$tag;
+  }
+  // Close remaining tags
+  while (count($stack) > 0) {
+    $output .= '</'. array_shift($stack) .'>';
+  }
+  return $output;
+}