The panel types `StreamFieldPanel`, `RichTextFieldPanel`, `ImageChooserPanel`, `DocumentChooserPanel` and `SnippetChooserPanel` have been phased out, and can now be replaced with `FieldPanel`. Additionally, `PageChooserPanel` is only required when passing a `page_type` or `can_choose_root`, and can otherwise be replaced with `FieldPanel`. In all cases, `FieldPanel` will now automatically select the most appropriate form element. This feature was developed by Matt Westcott.
[`FieldPanel`](wagtail.admin.panels.FieldPanel) now accepts a `permission` keyword argument to specify that the field should only be available to users with a given permission level. This feature was developed by Matt Westcott and sponsored by Google as part of Wagtail's page editor redevelopment.
* Major updates to frontend tooling; move Node tooling from Gulp to Webpack, upgrade to Node v16 and npm v8, eslint v8, stylelint v14 and others (Thibaud Colas)
* When Documents (e.g. PDFs) have been configured to be served inline via `WAGTAILDOCS_CONTENT_TYPES`&`WAGTAILDOCS_INLINE_CONTENT_TYPES` ensure that the filename is correctly set in the `Content-Disposition` header so that saving the files will use the correct filename (John-Scott Atlakson)
Various modules of Wagtail have been reorganised, and imports should be updated as follows:
* All modules under `wagtail.core` can now be found under `wagtail` - for example, `from wagtail.core.models import Page` should be changed to `from wagtail.models import Page`
* The `wagtail.tests` module is renamed to `wagtail.test`
*`wagtail.admin.edit_handlers` is renamed to `wagtail.admin.panels`
*`wagtail.contrib.forms.edit_handlers` is renamed to `wagtail.contrib.forms.panels`
These changes can be applied automatically to your project codebase by running the following commands from the project root:
```console
wagtail updatemodulepaths --list # list the files to be changed without updating them
wagtail updatemodulepaths --diff # show the changes to be made, without updating files
wagtail updatemodulepaths # actually update the files
* IE11 support was officially dropped in Wagtail 2.15, as of this release there will no longer be a warning shown to users of this browser.
* Wagtail is fully compatible with Microsoft Edge, Microsoft’s replacement for Internet Explorer. You may consider using its `IE mode <https://docs.microsoft.com/en-us/deployedge/edge-ie-mode>`_ to keep access to IE11-only sites, while other sites and apps like Wagtail can leverage modern browser capabilities.
### Hallo legacy rich text editor has moved to an external package
* Hallo was deprecated in [Wagtail v2.0 (February 2018)](https://docs.wagtail.org/en/stable/releases/2.0.html#new-rich-text-editor) and has had only a minimal level of support since then.
* If you still require Hallo for your Wagtail installation, you will need to install the [Wagtail Hallo editor](https://github.com/wagtail/wagtail-hallo) legacy package.
* We encourage all users of the Hallo editor to take steps to migrate to the new Draftail editor as this external package is unlikely to have ongoing maintenance.
*`window.registerHalloPlugin` will no longer be created on the page editor load, unless the legacy package is installed.
Various changes have been made to the internal API for defining panel types, previously known as edit handlers. As noted above, the module `wagtail.admin.edit_handlers` has been renamed to `wagtail.admin.panels`, and `wagtail.contrib.forms.edit_handlers` is renamed to `wagtail.contrib.forms.panels`.
Additionally, the base `wagtail.admin.edit_handlers.EditHandler` class has been renamed to `wagtail.admin.panels.Panel`, and `wagtail.admin.edit_handlers.BaseCompositeEditHandler` has been renamed to `wagtail.admin.panels.PanelGroup`.
Template paths have also been renamed accordingly - templates previously within `wagtailadmin/edit_handlers/` are now located under `wagtailadmin/panels/`, and `wagtailforms/edit_handlers/form_responses_panel.html` is now at `wagtailforms/panels/form_responses_panel.html`.
Where possible, third-party packages that implement their own field panel types should be updated to allow using a plain `FieldPanel` instead, in line with Wagtail dropping its own special-purpose field panel types such as `StreamFieldPanel` and `ImageChooserPanel`. The steps for doing this will depend on the package's functionality, but in general:
* If the panel sets a custom template, your code should instead define [a `Widget` class](https://docs.djangoproject.com/en/stable/ref/forms/widgets/) that produces your desired HTML rendering.
* If the panel provides a `widget_overrides` method, your code should instead call [`register_form_field_override`](/extending/forms) so that the desired widget is always selected for the relevant model field type.
* If the panel provides a `get_comparison_class` method, your code should instead call `wagtail.admin.compare.register_comparison_class` to register the comparison class against the relevant model field type.
Within the `Panel` class, the methods `widget_overrides`, `required_fields` and `required_formsets` have been deprecated in favour of a new `get_form_options` method that returns a dict of configuration options to be passed on to the generated form class:
* Panels that define `required_fields` should instead return this value as a `fields` item in the dict returned from `get_form_options`
* Panels that define `required_formsets` should instead return this value as a `formsets` item in the dict returned from `get_form_options`
* Panels that define `widget_overrides` should instead return this value as a `widgets` item in the dict returned from `get_form_options`
The template context for panels derived from `BaseChooserPanel` has changed. `BaseChooserPanel` is deprecated and now functionally identical to `FieldPanel`; as a result, the context variable `is_chosen`, and the variable name given by the panel's `object_type_name` property, are no longer available on the template. The only available variables are now `field` and `show_add_comment_button`. If your template depends on these additional variables, you will need to pass them explicitly by overriding the `render_as_field` method.
### ModelAdmin forms must subclass `WagtailAdminModelForm`
When overriding the `get_form_class` method of a ModelAdmin `CreateView` or `EditView` to pass a custom form class, that form class must now inherit from `wagtail.admin.forms.models.WagtailAdminModelForm`. Passing a plain Django ModelForm subclass is no longer valid.
### Removed the `size` argument of the undocumented `wagtail.utils.sendfile_streaming_backend.was_modified_since` function
- The `size` argument was used to add a `length` parameter to the HTTP header.
- This was never part of the HTTP/1.0 and HTTP/1.1 specifications see [RFC7232](https://httpwg.org/specs/rfc7232.html#header.if-modified-since) and existed only as a an unofficial implementation in IE browsers.
