Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/modules/ckeditor/ckeditor.api.php

@@ -0,0 +1,60 @@
+<?php
+
+/**
+ * @file
+ * Documentation for CKEditor module APIs.
+ */
+
+use Drupal\editor\Entity\Editor;
+
+/**
+ * @addtogroup hooks
+ * @{
+ */
+
+/**
+ * Modify the list of available CKEditor plugins.
+ *
+ * This hook may be used to modify plugin properties after they have been
+ * specified by other modules.
+ *
+ * @param $plugins
+ *   An array of all the existing plugin definitions, passed by reference.
+ *
+ * @see CKEditorPluginManager
+ */
+function hook_ckeditor_plugin_info_alter(array &$plugins) {
+  $plugins['someplugin']['label'] = t('Better name');
+}
+
+/**
+ * Modify the list of CSS files that will be added to a CKEditor instance.
+ *
+ * Modules may use this hook to provide their own custom CSS file without
+ * providing a CKEditor plugin. This list of CSS files is only used in the
+ * iframe versions of CKEditor.
+ *
+ * Front-end themes (and base themes) can easily specify CSS files to be used in
+ * iframe instances of CKEditor through an entry in their .info file:
+ *
+ * @code
+ * ckeditor_stylesheets[] = css/ckeditor-iframe.css
+ * @endcode
+ *
+ * @param array &$css
+ *   An array of CSS files, passed by reference. This is a flat list of file
+ *   paths relative to the Drupal root.
+ * @param $editor
+ *   The text editor object as returned by editor_load(), for which these files
+ *   are being loaded. Based on this information, it is possible to load the
+ *   corresponding text format object.
+ *
+ * @see _ckeditor_theme_css()
+ */
+function hook_ckeditor_css_alter(array &$css, Editor $editor) {
+  $css[] = drupal_get_path('module', 'mymodule') . '/css/mymodule-ckeditor.css';
+}
+
+/**
+ * @} End of "addtogroup hooks".
+ */