diff --git a/lib/pluginlib.php b/lib/pluginlib.php
index 7cfd5d728db..f3ad54612b2 100644
--- a/lib/pluginlib.php
+++ b/lib/pluginlib.php
@@ -92,7 +92,8 @@ class plugin_manager {
      * Returns a tree of known plugins and information about them
      *
      * @param bool $disablecache force reload, cache can be used otherwise
-     * @return array
+     * @return array the array keys are frankenstyle component names, and
+     *      the values are the corresponding plugintype_interface information objects.
      */
     public function get_plugins($disablecache=false) {
 
@@ -120,12 +121,14 @@ class plugin_manager {
     }
 
     /**
-     * Returns list of plugins that define their subplugins and information about them
+     * Returns list of plugins that define their subplugins and the information
+     * about them from the db/subplugins.php file.
      *
      * At the moment, only activity modules can define subplugins.
      *
-     * @param double $disablecache force reload, cache can be used otherwise
-     * @return array
+     * @param bool $disablecache force reload, cache can be used otherwise
+     * @return array with keys like 'mod_quiz', and values the data from the
+     *      corresponding db/subplugins.php file.
      */
     public function get_subplugins($disablecache=false) {
 
@@ -211,6 +214,23 @@ class plugin_manager {
         }
     }
 
+    public function are_dependancies_satisfied($dependancies) {
+        $installedplugins = $this->get_plugins();
+
+        foreach ($dependancies as $component => $requiredversion) {
+            if (!array_key_exists($component, $installedplugins)) {
+                return false;
+            }
+
+            if ($requiredversion != ANY_VERSION and
+                    $installedplugins[$component]->versiondb < $requiredversion) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
     /**
      * Defines a white list of all plugins shipped in the standard Moodle distribution
      *
@@ -487,6 +507,13 @@ interface plugintype_interface {
      */
     public function get_status();
 
+    /**
+     * Get the list of other plugins that this plugin requires ot be installed.
+     * @return array with keys the frankenstyle plugin name, and values either
+     *      a version string (like '2011101700') or the constant ANY_VERSION.
+     */
+    public function get_other_required_plugins();
+
     /**
      * Returns the information about plugin availability
      *
@@ -563,6 +590,9 @@ abstract class plugintype_base {
     public $versiondb;
     /** @var int|float|string required version of Moodle core  */
     public $versionrequires;
+    /** @var array other plugins that this one depends on.
+     *  Lazy-loaded by {@link get_other_required_plugins()} */
+    public $dependancies = null;
     /** @var int number of instances of the plugin - not supported yet */
     public $instances;
     /** @var int order of the plugin among other plugins of the same type - not supported yet */
@@ -649,6 +679,29 @@ abstract class plugintype_base {
         }
     }
 
+    /**
+     * Initialise {@link $dependancies} to the list of other plugins (in any)
+     * that this one requires to be installed.
+     */
+    protected function load_other_required_plugins() {
+        $plugin = $this->load_version_php();
+        if (!empty($plugin->dependancies)) {
+            $this->dependancies = $plugin->dependancies;
+        } else {
+            $this->dependancies = array(); // By default, no dependancies.
+        }
+    }
+
+    /**
+     * @see plugintype_interface::get_other_required_plugins()
+     */
+    public function get_other_required_plugins() {
+        if (is_null($this->dependancies)) {
+            $this->load_other_required_plugins();
+        }
+        return $this->dependancies;
+    }
+
     /**
      * @see plugintype_interface::load_db_version()
      */
@@ -1228,6 +1281,32 @@ class plugintype_mod extends plugintype_base implements plugintype_interface {
     }
 }
 
+
+/**
+ * Class for question behaviours.
+ */
+class plugintype_qbehaviour extends plugintype_base implements plugintype_interface {
+
+    /**
+     * @see plugintype_base::load_other_required_plugins().
+     */
+    protected function load_other_required_plugins() {
+        parent::load_other_required_plugins();
+        if (!empty($this->dependancies)) {
+            return;
+        }
+
+        // Standard mechanism did not find anything, so try the legacy way.
+        global $CFG;
+        require_once($CFG->libdir . '/questionlib.php');
+        $required = question_engine::get_behaviour_required_behaviours($this->name);
+        foreach ($required as $other) {
+            $this->dependancies['qbehaviour_' . $other] = ANY_VERSION;
+        }
+    }
+}
+
+
 /**
  * Class for question types
  */
@@ -1243,6 +1322,24 @@ class plugintype_qtype extends plugintype_base implements plugintype_interface {
             $this->displayname = get_string($this->name, 'qtype_' . $this->name);
         }
     }
+
+    /**
+     * @see plugintype_base::load_other_required_plugins().
+     */
+    protected function load_other_required_plugins() {
+        parent::load_other_required_plugins();
+        if (!empty($this->dependancies)) {
+            return;
+        }
+
+        // Standard mechanism did not find anything, so try the legacy way.
+        global $CFG;
+        require_once($CFG->libdir . '/questionlib.php');
+        $required = question_bank::get_qtype($this->name)->requires_qtypes();
+        foreach ($required as $other) {
+            $this->dependancies['qtype_' . $other] = ANY_VERSION;
+        }
+    }
 }
 
 /**
diff --git a/lib/setuplib.php b/lib/setuplib.php
index 9b300c2e6b6..ac38d03602a 100644
--- a/lib/setuplib.php
+++ b/lib/setuplib.php
@@ -61,6 +61,12 @@ define('MATURITY_BETA',     100);   // feature complete, ready for preview and t
 define('MATURITY_RC',       150);   // tested, will be released unless there are fatal bugs
 define('MATURITY_STABLE',   200);   // ready for production deployment
 
+/**
+ * Special value that can be used in $plugin->dependencies in version.php files.
+ */
+define('ANY_VERSION', 'any');
+
+
 /**
  * Simple class. It is usually used instead of stdClass because it looks
  * more familiar to Java developers ;-) Do not use for type checking of