diff --git a/lib/AbstractPicoPlugin.php b/lib/AbstractPicoPlugin.php
index d361bba..eaa982a 100644
--- a/lib/AbstractPicoPlugin.php
+++ b/lib/AbstractPicoPlugin.php
@@ -38,9 +38,9 @@ abstract class AbstractPicoPlugin implements PicoPluginInterface
      *
      * @see PicoPluginInterface::isEnabled()
      * @see PicoPluginInterface::setEnabled()
-     * @var bool
+     * @var bool|null
      */
-    protected $enabled = true;
+    protected $enabled;
 
     /**
      * Boolean indicating if this plugin was ever enabled/disabled manually
@@ -99,11 +99,12 @@ abstract class AbstractPicoPlugin implements PicoPluginInterface
                 if ($pluginEnabled !== null) {
                     $this->setEnabled($pluginEnabled);
                 } elseif ($this->enabled) {
+                    $this->setEnabled($this->enabled, true, true);
+                } elseif ($this->enabled === null) {
                     // make sure dependencies are already fulfilled,
                     // otherwise the plugin needs to be enabled manually
                     try {
-                        $this->checkCompatibility();
-                        $this->checkDependencies(false);
+                        $this->setEnabled(true, false, true);
                     } catch (RuntimeException $e) {
                         $this->enabled = false;
                     }
diff --git a/lib/Pico.php b/lib/Pico.php
index f2ae45a..e93306a 100644
--- a/lib/Pico.php
+++ b/lib/Pico.php
@@ -486,14 +486,18 @@ class Pico
      *
      * See {@see Pico::loadComposerPlugins()} for details about plugins loaded
      * from `vendor/pico-plugin.php` (i.e. plugins that were installed using
-     * `composer`), and {@see Pico::loadLocalPlugins()} for details about
-     * plugins installed to {@see Pico::$pluginsDir}. Pico loads plugins from
-     * the filesystem only if {@see Pico::$enableLocalPlugins} is set to TRUE
+     * composer), and {@see Pico::loadLocalPlugins()} for details about plugins
+     * installed to {@see Pico::$pluginsDir}. Pico loads plugins from the
+     * filesystem only if {@see Pico::$enableLocalPlugins} is set to TRUE
      * (this is the default).
      *
      * Pico always loads plugins from `vendor/pico-plugin.php` first and
      * ignores conflicting plugins in {@see Pico::$pluginsDir}.
      *
+     * The official PicoDeprecated plugin must be loaded when plugins that use
+     * an older API version than Pico's API version ({@see Pico::API_VERSION})
+     * are loaded.
+     *
      * Please note that Pico will change the processing order when needed to
      * incorporate plugin dependencies. See {@see Pico::sortPlugins()} for
      * details.
@@ -513,14 +517,21 @@ class Pico
         if ($this->enableLocalPlugins) {
             $this->loadLocalPlugins($composerPlugins);
         }
+
+        if (!isset($this->plugins['PicoDeprecated']) && (count($this->plugins) !== count($this->nativePlugins))) {
+            throw new RuntimeException(
+                "Plugins using an older API than version " . static::API_VERSION . " found, "
+                . "but PicoDeprecated isn't loaded"
+            );
+        }
     }
 
     /**
      * Loads plugins from vendor/pico-plugin.php
      *
-     * This method loads all plugins installed using `composer` and Pico's
-     * `picocms/pico-installer` installer by reading the `pico-plugin.php` in
-     * composer's `vendor` dir.
+     * This method loads all plugins installed using composer and Pico's
+     * `picocms/composer-installer` installer by reading the `pico-plugin.php`
+     * in composer's `vendor` dir.
      *
      * @see Pico::loadPlugins()
      * @see Pico::loadLocalPlugins()
diff --git a/lib/PicoPluginInterface.php b/lib/PicoPluginInterface.php
index ff7de1d..13a30dd 100644
--- a/lib/PicoPluginInterface.php
+++ b/lib/PicoPluginInterface.php
@@ -70,11 +70,15 @@ interface PicoPluginInterface
     public function setEnabled($enabled, $recursive = true, $auto = false);
 
     /**
-     * Returns TRUE if this plugin is enabled, FALSE otherwise
+     * Returns a boolean indicating whether this plugin is enabled or not
+     *
+     * You musn't rely on the return value when Pico's `onConfigLoaded` event
+     * wasn't triggered on all plugins yet. This method might even return NULL
+     * then. The plugin's status might change later.
      *
      * @see PicoPluginInterface::setEnabled()
      *
-     * @return bool plugin is enabled (TRUE) or disabled (FALSE)
+     * @return bool|null plugin is enabled (TRUE) or disabled (FALSE)
      */
     public function isEnabled();
 
diff --git a/plugins/DummyPlugin.php b/plugins/DummyPlugin.php
index b6b83fe..effc980 100644
--- a/plugins/DummyPlugin.php
+++ b/plugins/DummyPlugin.php
@@ -33,11 +33,27 @@ class DummyPlugin extends AbstractPicoPlugin
     /**
      * This plugin is disabled by default
      *
-     * If you want to enable your plugin by default, simply remove this class
-     * property.
+     * Usually you should remove this class property (or set it to NULL) to
+     * leave the decision whether this plugin should be enabled or disabled by
+     * default up to Pico. If all the plugin's dependenies are fulfilled (see
+     * {@see self::$dependsOn}), Pico enables the plugin by default. Otherwise
+     * the plugin is silently disabled.
+     *
+     * If this plugin should never be disabled *silently* (e.g. when dealing
+     * with security-relevant stuff like access control, or similar), set this
+     * to TRUE. If Pico can't fulfill all the plugin's dependencies, it will
+     * throw an RuntimeException.
+     *
+     * If this plugin rather does some "crazy stuff" a user should really be
+     * aware of before using it, you can set this to FALSE. The user will then
+     * have to enable the plugin manually. However, if another plugin depends
+     * on this plugin, it might get enabled silently nevertheless.
+     *
+     * No matter what, the user can always explicitly enable or disable this
+     * plugin in Pico's config.
      *
      * @see AbstractPicoPlugin::$enabled
-     * @var bool
+     * @var bool|null
      */
     protected $enabled = false;