Index: modules/system/system.api.php
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.api.php,v
retrieving revision 1.20
diff -u -p -r1.20 system.api.php
--- modules/system/system.api.php	26 Feb 2009 07:30:28 -0000	1.20
+++ modules/system/system.api.php	7 Mar 2009 17:33:34 -0000
@@ -1636,5 +1636,51 @@ function hook_disable() {
 }
 
 /**
+ * Allow modules to modify a dynamic query before it is run.
+ *
+ * All dynamic SELECT queries are run throug hook_query_alter()
+ * immediately prior to execution.  That allows any module to
+ * make additions or alterations to the query object as needed.
+ *
+ * Most queries that are intended to be altered will have one
+ * or more query tags added to them.  If so, query_alter implementations
+ * can use hasTag(), hasAllTags(), and hasAnyTag() to determine
+ * if they should run.
+ * * Note that because $query is an object it does not need
+ * to be passed by reference.  There will still be only
+ * one instance of the object.  Also note that the type
+ * hint is optional, but if used it should always use
+ * only QueryAlterableInterface, not SelectQueryInterface.
+ *
+ * @see QueryAlterableInterface
+ * @see SelectQueryInterface
+ * @param $query
+ *   The query object to modify.
+ */
+function hook_query_alter(QueryAlterableInterface $query) {
+
+  if ($query->hasTag('database_test_alter_add_range')) {
+    $query->range(0, 2);
+  }
+}
+
+/**
+ * Alter queries that have a specific tag.
+ *
+ * This hook works identically to hook_query_alter(), but
+ * will only get called for queries that have been tagged
+ * with QUERY_TAG.
+ *
+ * @see hook_query_alter()
+ * @see QueryAlterableInterface
+ * @see SelectQueryInterface
+ * @param $query
+ *   The query object to modify.
+ */
+function hook_query_QUERY_TAG_alter(QueryAlterableInterface $query) {
+  $query->range();
+}
+
+/**
  * @} End of "addtogroup hooks".
  */