diff --git a/core/modules/taxonomy/taxonomy.module b/core/modules/taxonomy/taxonomy.module
index 8ac2f99..7962f68 100644
--- a/core/modules/taxonomy/taxonomy.module
+++ b/core/modules/taxonomy/taxonomy.module
@@ -1730,17 +1730,17 @@ function taxonomy_field_presave($entity_type, $entity, $field, $instance, $langc
 /**
  * Implements hook_node_insert().
  *
- * We are using node hooks instead of field hooks, because we are maintaining a
- * term to node relationship. For details, see http://drupal.org/node/1050466.
+ * This maintains the taxonomy index. The index lists all terms that are
+ * related to a given node entity, and is therefore maintained at the entity
+ * level.
  */
 function taxonomy_node_insert($node) {
   // We maintain a denormalized table of term/node relationships, containing
   // only data for current, published nodes.
   $status = NULL;
   if (variable_get('taxonomy_maintain_index_table', TRUE)) {
-    // People are allowed to invoke node_save() without status and sticky, and
-    // in that case the original values are in $node->original. For instance,
-    // see NodeRevisionsTestCase().
+    // If a node property is not set in the node object when node_save() is
+    // called, the old value from $node->original is used.
     if (!empty($node->original)) {
       $status = (int)(!empty($node->status) || (!isset($node->status) && !empty($node->original->status)));
       $sticky = (int)(!empty($node->sticky) || (!isset($node->sticky) && !empty($node->original->sticky)));
@@ -1750,14 +1750,16 @@ function taxonomy_node_insert($node) {
       $sticky = (int)(!empty($node->sticky));
     }
   }
+  // We only maintain the taxonomy index for unpublished nodes.
   if ($status) {
-    // Collect all the terms.
+    // Collect a unique list of all the term IDs.
     $tid_all = array();
     foreach (field_info_instances('node', $node->type) as $instance) {
       $field_name = $instance['field_name'];
       $field = field_info_field($field_name);
       if ($field['module'] == 'taxonomy' && $field['storage']['type'] == 'field_sql_storage') {
-        // Same as status and sticky, the fields can be in $node->original.
+        // If a field value is not set in the node object when node_save() is
+        // called, the old value from $node->original is used.
         if (isset($node->{$field_name})) {
           $items = $node->{$field_name};
         }
@@ -1776,7 +1778,7 @@ function taxonomy_node_insert($node) {
         }
       }
     }
-    // Insert index for all the terms.
+    // Insert index entries for all the node's terms.
     if (!empty($tid_all)) {
       $query = db_insert('taxonomy_index')->fields(array('nid', 'tid', 'sticky', 'created'));
       foreach ($tid_all as $tid) {
@@ -1796,8 +1798,7 @@ function taxonomy_node_insert($node) {
  * Implements hook_node_update().
  */
 function taxonomy_node_update($node) {
-  // We don't maintain index for unpublished nodes, so we always rebuild the
-  // index to avoid too much checking.
+  // Always rebuild the node's taxonomy index entries on node save.
   taxonomy_node_delete($node);
   taxonomy_node_insert($node);
 }
diff --git a/core/modules/taxonomy/taxonomy.test b/core/modules/taxonomy/taxonomy.test
index 577a6cd..d874e4f 100644
--- a/core/modules/taxonomy/taxonomy.test
+++ b/core/modules/taxonomy/taxonomy.test
@@ -829,26 +829,29 @@ class TaxonomyTermTestCase extends TaxonomyWebTestCase {
 }
 
 /**
- * Tests the hook implementations that maintain the index of term tid to node
- * nid works as expected.
+ * Tests the hook implementations that maintain the taxonomy index.
  */
 class TaxonomyTermIndexTestCase extends TaxonomyWebTestCase {
 
   public static function getInfo() {
     return array(
       'name' => 'Taxonomy term index',
-      'description' => 'Tests the hook implementations that maintain the index of term tid to node nid works as expected.',
+      'description' => 'Tests the hook implementations that maintain the taxonomy index.',
       'group' => 'Taxonomy',
     );
   }
 
   function setUp() {
     parent::setUp('taxonomy');
+
+    // Create an administrative user.
     $this->admin_user = $this->drupalCreateUser(array('administer taxonomy', 'bypass node access'));
     $this->drupalLogin($this->admin_user);
-    $this->vocabulary = $this->createVocabulary();
 
-    $this->field_name_1 = drupal_strtolower($this->randomName());
+    // Create a vocabulary and add two term reference fields to article nodes.
+    $this->vocabulary = $this->createVocabulary();
+ 
+   $this->field_name_1 = drupal_strtolower($this->randomName());
     $this->field_1 = array(
       'field_name' => $this->field_name_1,
       'type' => 'taxonomy_term_reference',
@@ -910,7 +913,7 @@ class TaxonomyTermIndexTestCase extends TaxonomyWebTestCase {
   }
 
   /**
-   * Main test function.
+   * Tests that the taxonomy index is maintained properly.
    */
   function testTaxonomyIndex() {
     // Create terms in the vocabulary.
@@ -1028,7 +1031,7 @@ class TaxonomyTermIndexTestCase extends TaxonomyWebTestCase {
 }
 
 /**
- * Tests for multiple free-tagging fields referencing to a same vocabulary.
+ * Tests for multiple free-tagging fields using a single vocabulary.
  */
 class TaxonomyTermTaggingTestCase extends TaxonomyWebTestCase {
 
@@ -1042,8 +1045,11 @@ class TaxonomyTermTaggingTestCase extends TaxonomyWebTestCase {
 
   function setUp() {
     parent::setUp('taxonomy');
+    // Create an administrative user.
     $this->admin_user = $this->drupalCreateUser(array('administer taxonomy', 'bypass node access'));
     $this->drupalLogin($this->admin_user);
+
+    // Create a vocabulary and add two autocomplete fields on article nodes.
     $this->vocabulary = $this->createVocabulary();
 
     $this->field_name_1 = drupal_strtolower($this->randomName());
@@ -1108,7 +1114,7 @@ class TaxonomyTermTaggingTestCase extends TaxonomyWebTestCase {
   }
 
   /**
-   * Main test function.
+   * Tests creation, update, and deletion of terms in autocomplete fields.
    */
   function testTaxonomyTagging() {
     $term_name = $this->randomName();