Extending the Hallo Editor
==========================

.. warning::
  **As of Wagtail 2.0, the hallo.js editor is deprecated.** We have no intentions to remove it from Wagtail as of yet, but it will no longer receive bug fixes. Please be aware of the `known hallo.js issues <https://github.com/wagtail/wagtail/issues?q=is%3Aissue+is%3Aclosed+hallo+label%3A%22component%3ARich+text%22+label%3Atype%3ABug+label%3A%22status%3AWont+Fix%22>`_ should you want to keep using it.

  To use hallo.js on Wagtail 2.x, add the following to your settings:

  .. code-block:: python

    WAGTAILADMIN_RICH_TEXT_EDITORS = {
        'default': {
            'WIDGET': 'wagtail.admin.rich_text.HalloRichTextArea'
        }
    }

The legacy hallo.js editor’s functionality can be extended through plugins. For information on developing custom ``hallo.js`` plugins, see the project's page: https://github.com/bergie/hallo

Once the plugin has been created, it should be registered through the feature registry's ``register_editor_plugin(editor, feature_name, plugin)`` method. For a ``hallo.js`` plugin, the ``editor`` parameter should always be ``'hallo'``.

A plugin ``halloblockquote``, implemented in ``myapp/js/hallo-blockquote.js``, that adds support for the ``<blockquote>`` tag, would be registered under the feature name ``block-quote`` as follows:

.. code-block:: python

    from wagtail.admin.rich_text import HalloPlugin
    from wagtail.core import hooks

    @hooks.register('register_rich_text_features')
    def register_embed_feature(features):
        features.register_editor_plugin(
            'hallo', 'block-quote',
            HalloPlugin(
                name='halloblockquote',
                js=['myapp/js/hallo-blockquote.js'],
            )
        )

The constructor for ``HalloPlugin`` accepts the following keyword arguments:

 * ``name`` - the plugin name as defined in the JavaScript code. ``hallo.js`` plugin names are prefixed with the ``"IKS."`` namespace, but the name passed here should be without the prefix.
 * ``options`` - a dictionary (or other JSON-serialisable object) of options to be passed to the JavaScript plugin code on initialisation
 * ``js`` - a list of JavaScript 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
 * ``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

When writing the front-end code for the plugin, Wagtail’s Hallo implementation offers two extension points:

* In JavaScript, use the ``[data-hallo-editor]`` attribute selector to target the editor, eg. ``var $editor = $('[data-hallo-editor]');``.
* In CSS, use the ``.halloeditor`` class selector.


.. _whitelisting_rich_text_elements:

Whitelisting rich text elements
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

After extending the editor to support a new HTML element, you'll need to add it to the whitelist of permitted elements - Wagtail's standard behaviour is to strip out unrecognised elements, to prevent editors from inserting styles and scripts (either deliberately, or inadvertently through copy-and-paste) that the developer didn't account for.

Elements can be added to the whitelist through the feature registry's ``register_converter_rule(converter, feature_name, ruleset)`` method. When the ``hallo.js`` editor is in use, the ``converter`` parameter should always be ``'editorhtml'``.

The following code will add the ``<blockquote>`` element to the whitelist whenever the ``block-quote`` feature is active:

.. code-block:: python

    from wagtail.admin.rich_text.converters.editor_html import WhitelistRule
    from wagtail.core.whitelist import allow_without_attributes

    @hooks.register('register_rich_text_features')
    def register_blockquote_feature(features):
        features.register_converter_rule('editorhtml', 'block-quote', [
            WhitelistRule('blockquote', allow_without_attributes),
        ])

``WhitelistRule`` is passed the element name, and a callable which will perform some kind of manipulation of the element whenever it is encountered. This callable receives the element as a `BeautifulSoup <http://www.crummy.com/software/BeautifulSoup/bs4/doc/>`_ Tag object.

The ``wagtail.core.whitelist`` module provides a few helper functions to assist in defining these handlers: ``allow_without_attributes``, a handler which preserves the element but strips out all of its attributes, and ``attribute_rule`` which accepts a dict specifying how to handle each attribute, and returns a handler function. This dict will map attribute names to either True (indicating that the attribute should be kept), False (indicating that it should be dropped), or a callable (which takes the initial attribute value and returns either a final value for the attribute, or None to drop the attribute).
