diff -u b/core/modules/search/lib/Drupal/search/SearchQuery.php b/core/modules/search/lib/Drupal/search/SearchQuery.php
--- b/core/modules/search/lib/Drupal/search/SearchQuery.php
+++ b/core/modules/search/lib/Drupal/search/SearchQuery.php
@@ -15,20 +15,10 @@
 /**
  * Performs a query on the full-text search index for a word or words.
  *
- * This function is normally only called by each plugin that supports the
- * indexed search.
+ * This query is used by search plugins that use the search index (not all
+ * search plugins do, as some use a different searching mechanism).
  *
- * Results are retrieved in two logical passes. However, the two passes are
- * joined together into a single query, and in the case of most simple queries
- * the second pass is not even used.
- *
- * The first pass selects a set of all possible matches, which has the benefit
- * of also providing the exact result set for simple "AND" or "OR" searches.
- *
- * The second portion of the query further refines this set by verifying
- * advanced text conditions (such as negative or phrase matches).
- *
- * The used query object has the tag 'search_$type' and can be further
+ * The query object is given the tag 'search_$type' and can be further
  * extended with hook_query_alter().
  */
 class SearchQuery extends SelectExtender {
@@ -42,9 +32,8 @@
   /**
    * The type of search (search type).
    *
-   * This maps to the value of the type column in search_index, and is equal
-   * to the machine-readable name of the entity type being indexed, or other
-   * identifier provided by a search plugin.
+   * This maps to the value of the type column in search_index, and is usually
+   * equal to the machine-readable name of the search plugin.
    *
    * @var string
    */
@@ -58,7 +47,7 @@
   protected $keys = array('positive' => array(), 'negative' => array());
 
   /**
-   * Indicates whether the first pass query requires complex conditions (LIKE).
+   * Indicates whether the query conditions are simple or complex (LIKE).
    *
    * @var bool
    */
@@ -67,8 +56,8 @@
   /**
    * Conditions that are used for exact searches.
    *
-   * This is always used for the second pass query but not for the first pass,
-   * unless $this->simple is FALSE.
+   * This is always used for the second step in the query, but it is not part
+   * of the preparation step unless $this->simple is FALSE.
    *
    * @var DatabaseCondition
    */
@@ -93,16 +82,16 @@
   /**
    * Multiplier for the normalized search score.
    *
-   * This value is calculated by the first pass query and multiplied with the
-   * actual score of a specific word to make sure that the resulting calculated
-   * score is between 0 and 1.
+   * This value is calculated by preparation step and multiplied by the actual
+   * score of a specific word to make sure that the resulting calculated score
+   * is between 0 and 1.
    *
    * @var float
    */
   protected $normalize;
 
   /**
-   * Indicates whether the first pass query has been executed.
+   * Indicates whether the preparation step has been executed.
    *
    * @var bool
    */
@@ -134,8 +123,8 @@
   /**
    * Whether or not search expressions were ignored.
    *
-   * The maximum number of AND/OR combinations exceeded can be configured to
-   * avoid Denial-of-Service attacks. Expressions beyond the limit are ignored.
+   * The maximum number of AND/OR combinations can be configured to avoid
+   * Denial-of-Service attacks. Expressions beyond the limit are ignored.
    *
    * @var bool
    */
@@ -162,7 +151,12 @@
   /**
    * Parses the search query into SQL conditions.
    *
-   * We build two queries that match the dataset bodies.
+   * Sets up the following variables:
+   * - $this->keys
+   * - $this->words
+   * - $this->conditions
+   * - $this->simple
+   * - $this->matches
    */
   protected function parseSearchExpression() {
     // Matchs words optionally prefixed by a dash. A word in this case is
@@ -290,7 +284,11 @@
   }
 
   /**
-   * Helper function for parseQuery().
+   * Parses a word or phrase for parseQuery().
+   *
+   * Splits a phrase into words. Adds its words to $this->words, if it is not
+   * already there. Returns a list containing the number of new words found,
+   * and the total number of words in the phrase.
    */
   protected function parseWord($word) {
     $num_new_scores = 0;
@@ -312,9 +310,9 @@
   }
 
   /**
-   * Prepares and normalizes the query.
+   * Prepares the query and calculates the normalization factor.
    *
-   * After the query is normalised the keywords are weighted to give the results
+   * After the query is normalized the keywords are weighted to give the results
    * a relevancy score. The query is ready for execution after this.
    *
    * @return bool
@@ -332,6 +330,7 @@
     }
     $this->executedPrepare = TRUE;
 
+    // Build the basic search query.
     if (!empty($this->words)) {
       $or = db_or();
       foreach ($this->words as $word) {
@@ -339,7 +338,6 @@
       }
       $this->condition($or);
     }
-    // Build query for keyword normalization.
     $this->join('search_total', 't', 'i.word = t.word');
     $this
       ->condition('i.type', $this->type)
@@ -347,18 +345,18 @@
       ->groupBy('i.sid')
       ->having('COUNT(*) >= :matches', array(':matches' => $this->matches));
 
-    // Clone the query object to do the firstPass query;
-    $first = clone $this->query;
+    // Clone the query object to calculate the normalization factor.
+    $normalize_query = clone $this->query;
 
-    // For complex search queries, add the LIKE conditions to the first pass query.
+    // For complex search queries, add the LIKE conditions.
     if (!$this->simple) {
-      $first->join('search_dataset', 'd', 'i.sid = d.sid AND i.type = d.type');
-      $first->condition($this->conditions);
+      $normalize_query->join('search_dataset', 'd', 'i.sid = d.sid AND i.type = d.type');
+      $normalize_query->condition($this->conditions);
     }
 
-    // Calculate maximum keyword relevance, to normalize it.
-    $first->addExpression('SUM(i.score * t.count)', 'calculated_score');
-    $this->normalize = $first
+    // The normalization factor is the total of all search scores.
+    $normalize_query->addExpression('SUM(i.score * t.count)', 'calculated_score');
+    $this->normalize = $normalize_query
       ->range(0, 1)
       ->orderBy('calculated_score', 'DESC')
       ->execute()
@@ -419,13 +417,12 @@
   /**
    * Executes the search.
    *
-   * If not already done, this executes the first pass query. Then the complex
-   * conditions are applied to the query including score expressions and
-   * ordering.
-   *
-   * @return boolean
-   *   FALSE if the first pass query returned no results, and a database result
-   *   set if there were results.
+   * If not already done, this prepares and normalizes the query. Then the
+   * complex conditions are applied to the query including score expressions
+   * and ordering.
+   *
+   * @return
+   *   A query result set containing the results of the search query.
    */
   public function execute() {
     if (!$this->executedPrepare) {
@@ -490,7 +487,7 @@
     // Clone the inner query.
     $inner = clone $this->query;
 
-    // Add conditions to query.
+    // Add conditions to the query.
     $inner->join('search_dataset', 'd', 'i.sid = d.sid AND i.type = d.type');
     $inner->condition($this->conditions);
 
@@ -501,7 +498,7 @@
     $expressions =& $inner->getExpressions();
     $expressions = array();
 
-    // Add the sid as the only field and count them as a subquery.
+    // Add sid as the only field and count them as a subquery.
     $count = db_select($inner->fields('i', array('sid')), NULL, array('target' => 'slave'));
 
     // Add the COUNT() expression.