Move "default features" section out of Hallo-only docs

docs/advanced_topics/customisation/page_editing_interface.rst

@@ -93,7 +93,15 @@ Adding new features to this list is generally a two step process:
 
 Both of these steps are performed through the ``register_rich_text_features`` hook (see :ref:`admin_hooks`). The hook function is triggered on startup, and receives a *feature registry* object as its argument; this object keeps track of the behaviours associated with each feature identifier.
 
-This process for adding new features is described in the following sections.
+To have a feature active by default (i.e. on ``RichTextFields`` that do not define an explicit ``features`` list), add it to the ``default_features`` list on the ``features`` object:
+
+.. code-block:: python
+
+    @hooks.register('register_rich_text_features')
+    def register_blockquote_feature(features):
+        features.default_features.append('strikethrough')
+
+The process for creating new features is described in the following sections.
 
 
 .. _extending_wysiwyg:
@@ -148,20 +156,6 @@ The constructor for ``HalloPlugin`` accepts the following keyword arguments:
  * ``css`` - a dictionary of CSS files to be imported for this plugin, defined in the same way as a `Django form media <https://docs.djangoproject.com/en/1.11/topics/forms/media/>`_ definition
  * ``order`` - an index number (default 100) specifying the order in which plugins should be listed, which in turn determines the order buttons will appear in the toolbar
 
-To have a feature active by default (i.e. on ``RichTextFields`` that do not define an explicit ``features`` list), add it to the ``default_features`` list on the ``features`` object:
-
-.. code-block:: python
-
-    from django.utils.html import format_html
-
-    @hooks.register('register_rich_text_features')
-    def register_blockquote_feature(features):
-        features.register_editor_plugin(
-            'hallo', 'block-quote',
-            # ...
-        )
-        features.default_features.append('block-quote')
-
 
 .. _whitelisting_rich_text_elements: