update

Reviewed-on: #7

Event object compatibilty status.md

@@ -0,0 +1,48 @@
+This document describes what Event object implementations of existing services look like, how they differ and why and what could and should be improved.
+
+## Gancio
+
+```diff
+{
+  "id": "https://gancio-test.event-federation.eu/federation/m/1",
+  "name": "Test Event",
+  "url": "https://gancio-test.event-federation.eu/event/test-event",
+  "type": "Event",
+  "startTime": "2024-01-18T12:10:00.000+01:00",
+  "endTime": "2024-01-18T18:30:00.000+01:00",
+  "location": {
+    "type": "Place"
+    "name": "Gmota",
+    "address": "Münzgragebenstraße 21, 8010 Graz",
+    "latitude": null,
+    "longitude": null
+  },
+  "attachment": [],
+  "tag": [],
+  "published": "2023-10-13T09:56:25.858Z",
+  "attributedTo": "https://gancio-test.event-federation.eu/federation/u/ganciofortesting",
+  "to": [
+    "https://www.w3.org/ns/activitystreams#Public"
+  ],
+  "cc": [
+    "https://gancio-test.event-federation.eu/federation/u/ganciofortesting/followers"
+  ],
+-	"content": "\n    📍 Gmota\n    📅 Thursday, 18 January (12:10)\n    \n    This is an awesome test event! Do not miss it!\n\n\n\nFor sure!\n",
++ "content": "This is an awesome test event! Do not miss it!\n\n\n\nFor sure!\n",
+  "summary": "\n    📍 Gmota\n    📅 Thursday, 18 January (12:10)\n    \n    This is an awesome test event! Do not miss it!\n\n\n\nFor sure!\n",
+  "@context": [
+-   "https://www.w3.org/ns/activitystreams"
++   "https://www.w3.org/ns/activitystreams",
++     {
++       "sc": "http://schema.org/",
++       "address": {
++         "@id": "sc:address",
++         "@type": "sc:Text"
++     },
++   }
+  ]
+}
+```
+
+The schema stuff got merged right ahead:
+https://framagit.org/les/gancio/-/commit/9e1c2c2371e50dd1dbda32b92d5c45e4c0eb0900

Interoperability/architecture design proposal.md

@@ -0,0 +1,243 @@
+---
+gitea: none
+title: WordPress/ActivityPub
+authors:
+  - André Menrath
+  - ruruLanguageTool Linter
+include_toc: true
+---
+
+This document outlines suggestions for the further development of the WordPress ActivityPub plugin regarding its interoperability with other WordPress plugins that could enhance ActivityPub functionality.
+
+
+# Terms used 
+
+The following terms are used:
+
+## Content related
+- **post type:** post types and custom post types within WordPress
+- **object type:** ActivityPub [object type](https://www.w3.org/TR/activitystreams-vocabulary/#object-types)
+- **transformers:** a piece of code that converts items of particular WordPress post types to an ActivityPub object. For example a transformer that can transform:
+    - every post type to a `Note`
+    - `post` or `page` to `Note`, `Article`, `Image`, `Audio` or `Article` depending on the [post-format](https://wordpress.org/documentation/article/post-formats/)
+    - `tribe_events` (Event post the of [The Event Calendar](https://wordpress.org/plugins/the-events-calendar/)) to `Event`
+    - `podcast` (Podcast post of [Podlove Podcast Publisher](https://github.com/podlove/podlove-publisher)) to `PodcastEpisode` (as proposed and [implemented by Castopod](https://code.castopod.org/adaures/castopod/-/blob/main/app/Libraries/PodcastEpisode.php))
+
+## Actor related
+- **actors:** ActivityPub [Actor Objects](https://www.w3.org/TR/activitypub/#actor-objects)
+- **actor types:** ActivityPub [Actor Types](https://www.w3.org/TR/activitystreams-vocabulary/#actor-types)
+- **WordPress actor types:** Things on WordPress that can be mapped to actors, e.g.:
+    - WordPress users →`Person`
+    - Whole Blog →`Application` or `Group`
+    - Post types → e.g., `Organization`
+- **Actor mapper:** Describes the mapping of WordPress actor types to any ActivityPub actors.
+
+## General
+- **publish/dispatch:** Sending a `Create`, `Update` or `Announce` [Activity](https://www.w3.org/TR/activitypub/#create-activity-outbox).
+
+
+# Principals of the changes proposed to the ActivityPub plugin
+
+The WordPress ActivityPub plugin
+- should be aware (or even control) the whole chain from creating some content within WordPress to being published via ActivityPub. For sure, it should be the only plugin that directly sends and receives ActivityPub.
+- should not get any more complex by default, the out-of-the box functionality/features and simplicity should be similar to version 1.0.0.
+- offers other plugins the possibility to register custom transformers.
+- (maybe) offers other plugins the possibility to register new WordPress actor types, e.g. the `tribe_organizer` post type of [The Event Calendar](https://wordpress.org/plugins/the-events-calendar/).
+- handles the controls collisions of actor names:
+    * collisions that are already present during activation of a WordPress actor type on the settings page
+    * collisions that happen afterwards (e.g., a new user registering with the same username as the blog-wide actor)
+    * (maybe) show notifications/warnings when using an actor name which has been used and followed by in the past, as there may be issues due to caching of the old public key.
+- maybe distinguishes between the default user interface and advanced sections which give the user more fine-grained control:
+    * transformer management
+    * actor management
+
+
+# Goals
+
+## Goals of the WordPress Event Federation project
+The aim of the event federations project is to enable seamless federation of events created within an event plugin as an ActivityPub object with Type `Event` and accompanying meta-data, as typically seen in common ActivityPub implementations like Mobilizon. This will guarantee optimal compatibility between various services.
+
+## Tangential Objectives:
+Nevertheless, we see a lot of other cases that can benefit, if the primary goals of the Event Federation project are achieved this using a modularized approach as proposed below. The following list indicates examples what might be those other benefits:
+- Other types of content get federated in a more feature rich way:
+  - `PodcastEpisode` [as proposed by CastoPod](https://code.castopod.org/adaures/castopod/-/blob/main/app/Libraries/PodcastEpisode.php)
+  - `Question`
+  - `Product`
+  - …
+- ActivityPub offers features how to deal with multilingual content ([contentMap - see Example 115](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-contentmap)) which could be implemented differently by multilingual and translation plugins (example search for the current use of `->set_content_map` within the ActivityPub plugin). 
+
+**Note:** CastoPod, to give an example, has currently decided that podcast episodes will not be sent to followers as a `Create` activity directly containing the `PodcastEpisode` object, but will send a `Note` which is linking to the `PodcastEpisode`, because most Fediverse implementations currently ignore by default all object types they don't know. This is likely the same reason [flohmarkt](https://codeberg.org/grindhold/flohmarkt) is currently also using the `Note` and not `Product` even though that one would be available in the official specification.
+
+
+# Transformer Management
+
+## Current situation
+
+### Frontend
+The admin user interface in v1.0.0 lets one choose to which object type all post get transformed to. The options are:
+* [x] Note (default) — Should work with most platforms.
+* [ ] Article — The presentation of the "Article" might change on different platforms.
+* [ ] WordPress Post-Format — Maps the WordPress Post-Format to the ActivityPub Object Type. 
+
+### Backend
+Currently, all this functionality is handled via one hard-coded transformer in `includes/transformer/class post.php` ([Source](https://github.com/Automattic/wordpress-activitypub/blob/master/includes/transformer/class-post.php)) and the actual logic that assigns the type is somewhere else.
+
+```php
+/**
+ * WordPress Post Transformer
+ *
+ * The Post Transformer is responsible for transforming a WP_Post object into different othe
+ * Object-Types.
+ *
+ * Currently supported are:
+ *
+ * - Activitypub\Activity\Base_Object
+ */
+class Post {
+    ...
+    	/**
+         * Transforms the WP_Post object to an ActivityPub Object
+         *
+         * @see \Activitypub\Activity\Base_Object
+         *
+         * @return \Activitypub\Activity\Base_Object The ActivityPub Object
+         */
+        public function to_object() {
+    ...
+```
+
+## Proposal
+All publicly accessible WordPress post types can become active for ActivityPub federation when selecting a transformer available for the relevant post type. **It is up to the transformer to determine the target ActivityPub object type**, which may vary depending on variables such as post type or post format. If there is no specific transformer available for a given post type, it cannot be assigned through the user interface. 
+
+### Frontend
+|                   | Note | Post-Format | The Events Calendar Transformer | Custom Event Transformer |
+| ----------------- |:----:|:-----------:|:-------------------------------:|:------------------------:|
+| **post**          | X    | O           | -                               | -                        |
+| **page**          | O    | O           | -                               | -                        |
+| **tribe_events**  | O    | -           | X                               | O                        |
+| **custom_event**  | O    | -           | -                               | O                        |
+| **…**             | O    | -           | -                               | -                        |
+
+**columns:** Available transformers  
+**rows:** Public and non-password protected WordPress post types  
+**Note:** Only one or zero selections can be made in each row.  
+
+
+- For any custom post type, if there is a custom transformer registered, indicate that one should be selected as default (or select it right ahead?).
+- Should not differ too much from the current view: Maybe completely hide the current activity object type part of the settings and only show the buttons for `enable` and `disable` and move the transformer table to an advanced settings page.
+- Maybe make the tables more advanced and clearly show the origin of the transformer (built-in, etc.) and maybe a Pop-Up with a description, or even a link to a configuration page of the transformer.
+
+### Backend
+
+A solution could be to define a transformer interface and let the transformers be implementations.
+```php
+interface Transformer {
+    public function get_supported_post_types(): array;
+    public function get_transformer_info(): array;
+    public function to_object(WP_Post $post);
+    ....
+}
+```
+
+Use WordPress's hook system or a public API function to let other plugins register their custom transformer implementations to the ActivityPub plugin.
+
+**Problem:** With the design above the transformer does a lot and leaves a lot of responsibility to the developer implementing it.
+
+**Possible alternatives and solutions:**
+
+- The ActivityPub plugin could provide reusable Traits for common tasks.
+- Provide useful functions, documentation, and examples for automatic testing of transformers.
+- Highly unlikely: The ActivityPub plugin provides an even more high level framework for adding transformers. For example for events the ActivityPub plugin could provide a built-in transformer to the object type `Event` which only needs a mapping (might make things harder, instead of making them easier). See Appendix.
+- Highly unlikely: don't use an interface with implementations, (miss)use class extensions.
+
+
+# Mapping: Actors and Dispatching (early draft)
+
+More comprehensive actor management would benefit our project aims and potentially meet the needs of others in the future. Nevertheless, **its importance is considerably lower than that of Transformer management**. In the future, the following factors may become more important when larger websites should be using the ActivityPub plugin.
+
+## Current situation
+Currently, the admin user interface in v1.0.0 gives very limited options.
+```
+- [ ] Enable `blog`-actor
+- [ ] Enable `author`-actors
+```
+Note that depending on which options are enabled, the method of federating via ActivityPub varies significantly:
+
+- If the `blog`-actor is enabled, but the `author`-actors are not, posts are attributed and created by the blog actor.
+- If both options are enabled the `blog`-actor will announce (boost) the posts of the `author`-actors.
+
+Currently, the whole logic controlling this is written within the `Activity_Dispatcher` [class](https://github.com/Automattic/wordpress-activitypub/blob/master/includes/class-activity-dispatcher.php#L21) which is currently triggered only within the `Scheduler` [class](https://github.com/Automattic/wordpress-activitypub/blob/master/includes/class-scheduler.php#L14-L15).
+Furthermore, although a blog actor is available, the ActivityPub plugin is still written in such a way that WordPress users are the default ActivityPub actors. This also reflects in things like the class which is responsible for the actor lookup is still called `Users` and yet handles the `Blog` and the `Application` user too, see the [Source](https://github.com/Automattic/wordpress-activitypub/blob/master/includes/collection/class-users.php).
+
+## Possibilities
+ActivityPub knows several [actor types](https://www.w3.org/TR/activitystreams-core/#actors):
+- `Application`
+- `Group`
+- `Organization`
+- `Person`
+- `Service`
+
+The ActivityPub specification allows for immense flexibility in its application. As WordPress websites fulfill a variety of tasks and objectives, it is **challenging to implement control features and options for actor management that are more capable without sacrificing user-friendliness.**
+
+## What features does our Event Federation project need?
+- For maximum Mobilizon compatibility we would love to have simply an actor of type `Application`, preferable called `@relay@wordpress.site`, that announces all events. Nonetheless, in theory, a Mobilizon instance should have the capability to follow any other actor as well. More or less this can already be achieved with the current blog-actor.
+- Additionally, for example, organizers in [The Event Calendar](https://wordpress.org/plugins/the-events-calendar/) could also offer their own actor of type `Organizer` or `Group` to publicize events (getting referred to via [attributedTo](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-attributedto)) if the `author`-actors are enabled, or create events (being the [actor](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-actor) directly) if the `author`-actors are not enabled.
+- Optional: As events are sometimes published a long time before they start, adding the possibility that events get announced again at a scheduled time before the start, e.g. by sending an `Announce` activity.
+
+## Other features
+Other WordPress actor types might have valid use cases, like actors for categories, or specific post types in general: "I only want to see the blog updates, but I do not want to spam my timeline with each product they post on their website, even if they choose to federate them."
+
+**Problems:**
+- Overall complexity may lead to programming and usage errors.
+- Naming collisions become more likely. See below.
+- Who is the `actor`, who is the `attributedTo`, who is just sending an `Announce` of a post?
+
+##  Proposed starting point for evaluating use cases
+We keep in mind that every post shall only ever be sent as a `Create` Activity once, by one single actor.
+Therefore when the ActivityPub plugin makes use of a certain WordPress actor type, the WordPress actor type must exactly return one actor, which may depend on the current post being published and on the user doing the action (latter information should also be available within the WP_Post object). 
+
+**User Interface:**
+
+|                  | User  | Event organizers | Product Relay |  Relay(Blog) | Categories |
+| -----------------|:-----:|:----------------:|:-------------:|:------------:|:----------:|
+| **post**         | C     | -                | -             | A            | A          |
+| **page**         | C     | -                | -             | A            | O          |
+| **tribe_events** | O     | C                | -             | A            | 0          |
+| **product**      | O     | -                | C             | 0            | 0          |
+ 
+**x:** Actor mapper 
+**y:** WordPress post types  
+**C:** `Create` — can only be assigned once per row  
+**A:** `Announce` — can be assigned multiple times per row, but only if a `Create` has been assigned before   
+
+- Only allow setting something to `Announce`, when a `Create` is already set.
+- Maybe forbid, that a user can automatically announce a post, because it's the "lowest level".
+
+## Actor collisions
+Each ActivityPub actor must have a [unique ID](https://www.w3.org/TR/activitypub/#obj-id). In our case this is an HTTPS URI.
+But in reality [webfinger](https://webfinger.net/) is used: `@actor-name@instance.tld`. Actors like Persons and Groups and Applications have public keys attached to them, as well as their ID is probably cached by most software. So assigning some actor-name to something new also can cause unintended behavior.
+
+If multiple plugins want to individually federate their content (like events, products, and blog posts or even the built-in WordPress categories), they must be able to have something like an actor API, the ActivityPub plugin can register. The ActivityPub plugin being the main coordinator is necessary because actors are globally unique. 
+- For existing (collision was created before the installation/activation of the plugin)
+- For new collisions (collision was/will be created after the installation/activation of the plugin)
+
+It seems like it is the best if collisions are avoided in the first place by encouraging the use of prefixes, like `category_<category>`.
+
+### Existing collisions
+- **Easy:** Either we just tell the user to resolve all conflicts before a WordPress actor type can be activated at all
+- **Complex:** We let him choose alternatives for conflicts.
+
+### New collisions
+- **Easy** Forbid the saving of new users or posts that would conflict with an existing actor.
+- **Complex** …
+
+## Conclusion
+- Anyway it seems the question has to be raised whether the ActivityPub plugin should store a history of all past and currently mapped actors.
+- Additionally, shouldn't the user have a detailed overview in each case if the actor management should get more complex? 
+  
+
+# Appendix
+
+## The approach of youtube-dl
+[youtube-dl](https://github.com/ytdl-org/youtube-dl) is solving a similar problem with "extractors" that return data to the processing-chain of youtube-dl. They provide a base class that includes useful functions for common issues e.g. automatic testing, geo-bypassing, login/cookie/header management. The most [basic extractor](https://github.com/ytdl-org/youtube-dl#adding-support-for-a-new-site) is about 40 lines of code.
+They can also chain extractors recursively, like a extractor for mastodon videos, that gets the video from the post and returns the source of the video, that could be YouTube, Vimeo or anything else youtube-dl supports.

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+
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+
+Section 6 – Term and Termination.
+
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+
+     b.	Where Your right to use the Licensed Material has terminated under Section 6(a), it reinstates:
+
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+
+          2. upon express reinstatement by the Licensor.
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+
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+
+Section 8 – Interpretation.
+
+     a.	For the avoidance of doubt, this Public License does not, and shall not be interpreted to, reduce, limit, restrict, or impose conditions on any use of the Licensed Material that could lawfully be made without permission under this Public License.
+
+     b.	To the extent possible, if any provision of this Public License is deemed unenforceable, it shall be automatically reformed to the minimum extent necessary to make it enforceable. If the provision cannot be reformed, it shall be severed from this Public License without affecting the enforceability of the remaining terms and conditions.
+
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+
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+
+Creative Commons may be contacted at creativecommons.org.

Transformers/add-transformer.md

@@ -0,0 +1,26 @@
+# Add New Transformer
+
+The WordPress ActivityPub plugin offers an advanced built-in transformer, but it also allows other plugins to register new transformers.
+
+## Hooks
+
+To do that we simply hook to the `activivitypub_transformer_register` action which provides access to the transformer manager as a parameter. Developers can use this manager to add new transformers using the `register()` method of this manager instance.
+
+## Registering Transformers
+
+To register new transformers use the following code:
+
+```php
+function register_new_transformers( $transformers_manager ) {
+
+	require_once( __DIR__ . '/activitypub/transformer/name-1.php' );
+	require_once( __DIR__ . '/activitypub/transformer/name-2.php' );
+
+	$transformers_manager->register( new \Transformer_1() );
+	$transformers_manager->register( new \Transformer_2() );
+
+}
+add_action( 'activivitypub_transformer_register', 'register_new_transformers' );
+```
+
+The transformer manager registers new transformers by accepting transformer instances. For more information about the transformer class, read about the [transformer class structure](./transformer-structure.md/).

Transformers/index.md

@@ -0,0 +1,23 @@
+# ActivityPub Transformers
+
+The WordPress ActivityPub plugin comes with a built-in transformer which lets you choose how your posts will look like in the Fediverse.
+
+## Managing Transformers
+
+Other plugins can register new transformers and unregister existing ones.
+
+* [Add New Transformer](./add-transformer.md/)
+* [Remove Transformer](./remove-transformer.md/)
+
+## Creating New Transformers
+
+Learn more about transformer anatomy and how to create your own:
+
+* [Transformer Structure](./transformer-structure.md/)
+
+
+## Code Examples
+
+See the following examples to see how easy it is.
+
+* [The Events Calendar](./the-events-calendar-example.md/)

Transformers/the-events-calendar-example.md

@@ -0,0 +1,115 @@
+## Folder Structure
+You need at least two files. One file for the transformer itself and one file for registering it.
+```
+activitypub-tribe-transformer/
+|
+├─ activitypub/
+|  └─ transformer/
+|     └─ tribe.php
+|
+└─ activitypub-tribe-transformer.php
+```
+
+## Plugin Files
+**activitypub-tribe-transformer-php**
+```php
+<?php
+/**
+ * Plugin Name: ActivityPub Transformer for The Events Calendar
+ * Description: Transforms tribe_event posts to ActivityPub object of type Event.
+ * Plugin URI:  https://event-federation.eu/
+ * Version:     1.0.0
+ * Author:      WordPress ActivityPub Enthusiast
+ * Author URI:  https://event-federation.eu
+ * Text Domain: activitypub-tribe-transformer
+ *
+    * ActivityPub tested up to: 1.2.0
+    */
+
+if ( ! defined( 'ABSPATH' ) ) {
+	exit; // Exit if accessed directly.
+}
+
+/**
+ * Register Tribe Transformer.
+ *
+ * Include transformer file and register transformer class.
+ *
+ * @since 1.0.0
+ * @param \Activitypub\Transformer\Transformers_Manager $transformers_manager ActivtiyPub transformers manager.
+ * @return void
+ */
+function register_tribe_transformer( $transformers_manager ) {
+	require_once( __DIR__ . '/activitypub/transformer/tribe.php' );
+	$transformers_manager->register( new \Tribe() );
+}
+
+add_action( 'activitypub_transformers_register', 'register_tribe_transformer' );
+```
+
+**activtiypub/transformer/tribe.php**
+```php
+<?php
+if ( ! defined( 'ABSPATH' ) ) {
+	exit; // Exit if accessed directly.
+}
+
+/**
+ * ActivityPub Tribe Transformer
+ *
+ * @since 1.0.0
+ */
+class Tribe extends \Activitypub\Transformer\Base {
+
+	/**
+	 * Get transformer name.
+	 *
+	 * Retrieve the static and prefixed transformer name for this transformer.
+	 *
+	 * @since 1.0.0
+	 * @access public
+	 * @return string Widget name.
+	 */
+	public function get_name() {
+		return 'activitypub-tribe-transformer/tribe';
+	}
+
+	/**
+	 * Get transformer title.
+	 *
+	 * Retrieve the transformer title.
+	 *
+	 * @since 1.0.0
+	 * @access public
+	 * @return string Widget title.
+	 */
+	public function get_label() {
+		return 'The Events Calendar';
+	}
+
+	/**
+	 * Returns the ActivityStreams 2.0 Object-Type for an Event.
+	 *
+	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-event
+	 *
+	 * @return string The Event Object-Type.
+	 */
+	protected function get_object_type() {
+		return 'Event';
+	}
+
+	/**
+	 * Get supported post types.
+	 *
+	 * Retrieve the list of supported WordPress post types this transformer widget can handle.
+	 *
+	 * @since 1.0.0
+	 * @access public
+	 * @return array Widget categories.
+	 */
+	public function get_supported_post_types() {
+		return [ 'tribe_events' ];
+	}
+
+}
+```

Transformers/transformer-structure.md

@@ -0,0 +1,38 @@
+# Transformer Structure
+
+To create a custom ActivityPub Transformer start by creating a class that extends the `\Activitypub\Transformer\Base` class and fill in all the required methods.
+
+Each transformer needs to have a few basic settings — a unique name that will identify the transformer, a label that will be used as the title when being displayed in the settings section, and a list of supported post types that the transformer can use as an input.
+
+## Transformer Class
+
+First, we need to create a class that extends the `\Activitypub\Transformer\Base` class:
+
+```php
+class Activitypub_Test_Transformer extends \Activitypub\Transformer\Base {
+}
+```
+
+## Transformer Methods
+
+A simple transformer skeleton class will look as follows:
+
+```php
+class Activitypub_Test_Transformer extends \Activitypub\Transformer\Base {
+	public function get_name() {}
+
+	public function get_label() {}
+
+	public function get_object_type() {}
+
+	public function supported_post_types() {}
+
+	public function to_object() {}
+
+	// TODO
+}
+```
+
+The `\Activitypub\Transformer\Base` class has many more methods, but the vast majority of your needs are covered by the methods mentioned above.
+
+// TODO

architecture design proposal.md

@@ -1,261 +0,0 @@
----
-gitea: none
-title: WordPress/ActivityPub
-lang: en
-authors:
-  - André Menrath
-  - ruru
-include_toc: true
----
-
-This document describes proposals for the evolvment of the [WordPress ActivityPub plugin](https://github.com/Automattic/WordPress-ActivityPub/) in the field of the interaction with other WordPress plugins that may add additional ActivityPub features.
-
-# Terms used 
-The following terms are used:
-
-## Actor related
-
-- **Actors:** ActivityPub [Actor Objects](https://www.w3.org/TR/activitypub/#actor-objects)
-- **Actor Types:** ActivityPub [Actor Types](https://www.w3.org/TR/activitystreams-vocabulary/#actor-types)
-- **WordPress actor types:** Things on WordPress that can be mapped to actors:
-    - WordPress users →`Person`
-    - Whole Blog →`Application` or `Group`
-    - post types → e.g. `Organization`
-    - custom definitions → custom actor types
-- **Mapping:** Which WordPress actor types are actually are mapped to any ActivityPub actors at all and to which one.
-
-## Content related
-
-- **post type:** Post type and custom post types within WordPress
-- **Object Type:** ActivityPub [object type](https://www.w3.org/TR/activitystreams-vocabulary/#object types)
-- **Transformers:** a piece of code that converts items of a particular WordPress post type to an ActivityPub object of (a) specified type(s). For example a transformer that can transform:
-    - `post` to a `Note`
-    - `post` to a `Article`
-    - `post` to `Note`, `Article`, `Image`, `Audio` or `Article` depending on the [post-format](https://wordpress.org/documentation/article/post-formats/)
-    - `tribe_events` (Event post the of [The Event Calendar](https://wordpress.org/plugins/the-events-calendar/)) to `Event`
-    - `podcast` (Podcast post of [Podlove Podcast Publisher](https://github.com/podlove/podlove-publisher)) to `PodcastEpisode` as ([proposed and implemented by Castopod](https://code.castopod.org/adaures/castopod/-/blob/main/app/Libraries/PodcastEpisode.php))
-
-## General
-
-- **publish/dispatch:** Sending a `Create`, `Update` or `Announce` [Activity](https://www.w3.org/TR/activitypub/#create-activity-outbox).
-
-
-# Principals of the changes proposed to the ActivityPub plugin
-The WordPress ActivityPub plugin
-- should be aware (or even control) the whole chain from creating some content within WordPress to being published via ActivityPub. For sure, it should be the only plugin that directly sends and receives ActivityPub.
-- should not get any more complex by default, the out-of-the box functionality/features and simplicity should be similar to version 1.0.0.
-- offers other plugins the possibility to register custom transformers.
-- (maybe) offers other plugins the possibility to register new WordPress actor types, e.g. the `tribe_organizer` post type of [The Event Calendar](https://wordpress.org/plugins/the-events-calendar/).
-- handles the controls collisions of actor names:
-    * collisions that are already present during activation of a WordPress actor type on the settings page
-    * collisions that happen afterwards (e.g. a new user registering with the same username as the blog-wide actor)
-    * (maybe) show notifications/warnings when using an actor name which has been used and followed by in the past, as there may be issues due to caching of the old public key.
-- maybe distinguishes between the default admin user interface and advanced sections which give the user more fine-grained control:
-    * transformer management
-    * actor management
-
-
-# Goals
-
-Our primary goal is to make it possible that events created within an event plugin can federate properly as an ActivityPub object with Type `Event` along with all the meta-data belonging to the event, as found in common ActivityPub implementations, e.g. of Mobilizon, in order to ensure maximum compatibly between those services.
-
-Nevertheless, we see a lot of other cases that can benefit, if we achieve this using a modularized approach as proposed below. The following list indicates examples what might be those other benefits:
-- Other types of content get federated in a more feature rich way:
-  - `PodcastEpisode` [as proposed by CastoPod](https://code.castopod.org/adaures/castopod/-/blob/main/app/Libraries/PodcastEpisode.php)
-  - `Question`
-  - `Product`
-  - ...
-- ActivityPub offers features how to deal with multilingual content ([contentMap - see Example 115](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-contentmap)) which could be implemented differently by multilingual and translation plugins (example search for the current use of `->set_content_map` within the ActivityPub plugin). 
-
-**Note:** CastoPop, to give an example, has currently decided that podcast episodes will not be sent to followers as a `Create` activity directly containing the `PodcastEpisode` object, but will send a `Note` which is linking to the `PodcastEpisode`, because most Fediverse implementations currently ignore by default all object types they don't know. This is likely the same reason [flohmarkt](https://codeberg.org/grindhold/flohmarkt) is currently also using the `Note` an not `Product` even though that one would be available in the offical specification.
-
-# Transformer Management
-
-## User Interface
-
-### Current situation
-
-The admin user interface in v1.0.0 lets one choose to which object type all post get transformed to. The options are:
-* [x] Note (default) - Should work with most platforms.
-* [ ] Article - The presentation of the "Article" might change on different platforms.
-* [ ] WordPress Post-Format - Maps the WordPress Post-Format to the ActivityPub Object Type. 
-
-### Proposal
-
-Every public WordPress post type may be transformed (have different transformers available) may convert it to an ActivityPub object. Transformations that are not 
-available for a given post type are greyed out in the user interface:
-
-|                   | Note | Article | Page | Event |
-| ----------------- |:----:|:-------:|:----:|:-----:|
-| **post**          | X    | O       | O    | -     |
-| **page**          | O    | X       | O    | -     |
-| **tribe_events**  | O    | -       | -    | X     |
-| **...**           | O    | -       | -    | -     |
-
-**x:** ActivityPub object types  
-**y:** WordPress post types  
-
-- For any custom post type, if there is a custom transformer registered, indicate that one should be selected as default (or select it right ahead?).
-- Should not differ too much from the current view: Maybe completely hide the current activity object type part of the settings and only show the buttons for `enable` and `disable` and move the transformer table to an advanced settings page.
-- Maybe make the tables more advanced and cleary show the origin of the transformer (built-in, etc.) and maybe a Pop-Up with a description.
-
-### Problems
-
-- If two transformers with the same source and target are installed, then we have two possibilities:
-  1. A dropdown menu is displayed to select one of the transformers.
-  2. Adding another column and maybe add indicators where the transformer comes from (e.g. `builtin`, `custom` or showing the source)
-
-- Should a transformer be always a many-to-one relationship or may it be a many-to-many one.
-
-- Highly unlikely: Do we really want to manage which transformers apply to what directly or do users prefer a setting like "let a certain plugin take care of this post type"? Then further configuration would have to be managed by the other plugins.
-
-## Backend
-
-Currently, only one hard-coded transformer exists in `includes/transformer/class post.php` ([Source](https://github.com/Automattic/wordpress-activitypub/blob/master/includes/transformer/class-post.php)).
-
-```php
-/**
- * WordPress Post Transformer
- *
- * The Post Transformer is responsible for transforming a WP_Post object into different othe
- * Object-Types.
- *
- * Currently supported are:
- *
- * - Activitypub\Activity\Base_Object
- */
-class Post {
-    ...
-    	/**
-         * Transforms the WP_Post object to an ActivityPub Object
-         *
-         * @see \Activitypub\Activity\Base_Object
-         *
-         * @return \Activitypub\Activity\Base_Object The ActivityPub Object
-         */
-        public function to_object() {
-    ...
-```
-
-A solution could be to define a transformer interface and let the transformers be implementations.
-```php
-interface Transformer {
-    public function get_supported_post_types(): array;
-    public function get_target_activitypub_object_type(): string;
-    public function to_object(WP_Post $post);
-    ....
-}
-```
-
-Use WordPress's hook system or a public API function to let other plugins register their custom transformer implementations to the ActivityPub plugin.
-
-**Problem:** With the design above the transformer does a lot and leaves a lot of responsibility to the developer implementing it.
-
-Possible alternatives and solutions:
-- The ActivityPub plugin could provide reusable Traits for common tasks.
-- The ActivityPub plugin provides an even more height level framework for adding transformers. For example for events the ActivityPub plugin could provide a built-in transformer to the object type `Event` which only needs a mapping (might make things harder, instead of making them easier). See Appendix.
-- Don't use an interface with implementations, (miss)use class extensions.
-
-
-# Mapping: Actors and Dispatching
-
-More comprehensive actor management would benefit our project aims and potentially meet the needs of others in the future. Nevertheless, **its importance is considerably lower than that of Transformer management**. In the future, the following factors may become more important when larger websites should be using the ActivityPub plugin.
-
-## Current situation
-Currently, the admin user interface in v1.0.0 gives very limited options.
-```
-- [ ] Enable `blog`-actor
-- [ ] Enable `author`-actors
-```
-Note that depending on which options are enabled, the method of federating via ActivityPub varies significantly:
-
-- If the `blog`-actor is enabled, but the `author`-actors are not, posts are attributed and created by the blog actor.
-- If both are enabled the `blog`-actor will announce (boosting) the posts of the 
-`author`-actors.
-
-Currently the whole logic controlling this is written within the `Activity_Dispatcher` [class](https://github.com/Automattic/wordpress-activitypub/blob/master/includes/class-activity-dispatcher.php#L21) which is currently triggered only within the `Scheduler` [class](https://github.com/Automattic/wordpress-activitypub/blob/master/includes/class-scheduler.php#L14-L15).
-
-## Possibilities
-ActivityPub knows several [actor types](https://www.w3.org/TR/activitystreams-core/#actors):
-- `Application`
-- `Group`
-- `Organization`
-- `Person`
-- `Service`
-
-The specifications allow for a lot of flexibility in their use. As WordPress websites serve a variety of tasks and goals, providing more detailed capabilities and options in this area **may prove challenging to accomplish in a user-friendly manner**.
-
-## What features does our event federation project need?
-
-- For maximum Mobilizon compatibility we would love to have simply an actor of type `Application`, preferable called `@relay@wordpress.site`, that announces all events. Nonetheless, in theory, a Mobilizon instance should have the capability to follow any other actor as well.
-
-- Additionally, for example, organizers in [The Event Calendar](https://wordpress.org/plugins/the-events-calendar/) could also offer their own actor of type `Organizer` or `Group` to publicize events, or create events if the `author`-actors are not enabled.
-
-- Optional: As events are sometimes published a long time before they start, adding the posibility that events get announced again at a scheduled time before the start, e.g. by sending an `Announce` activity.
-
-## Other features
-
-Other WordPress actor types might have valid use cases, like actors for categories, or specific post types in general: "I only want to see the blog updates, but I do not want to spam my timeline with each product they post on their site, even if they choose to federate them."
-
-**Problems:**
-- Overall complexity may lead to programming and usage errors.
-- Naming collisions become more likely. See below.
-- Who is the `actor`, who is the `attributedTo`, who is just sending an `Announce` of a post?
-
-##  Proposed starting point for evaluating use cases
-
-We keep in mind that every post type shall only ever send as a `Create` Activity once by one single actor.
-
-**User Interface:**
-
-|                  | users | tribe_organizers | custom |  blog | category |
-| -----------------|:-----:|:----------------:|:------:|:-----:|:--------:|
-| **post**         | C     | O                | O      | A     | A        |
-| **page**         | C     | O                | O      | A     | O        |
-| **tribe_events** | O     | C                | -      | A     | 0        |
-| **product**      | O     | -                | C      | 0     | 0        |
- 
-**x:** WordPress actor-types  
-**y:** WordPress post types  
-**C:** Create  
-**A:** Announce  
-**user:** the WordPress user publishing or updating something  
-**all:** blog-wide actor, everything that is published (like a relay)  
-**custom:** e.g. only a certain post_type that gets announced with this actor  
-**tribe_organizers:** only posts by one organizer  
-
-- Only allow setting something to `Announce`, when a `Create` is already set.
-- Maybe forbid, that a user can automatically announce a post, because it's the "lowest level". 
-
-## Actor collisions
-
-Each ActivityPub actor must have a [unique ID](https://www.w3.org/TR/activitypub/#obj-id). In our case this is a HTTPS URI.
-But in reality [webfinger](https://webfinger.net/) is used: `@actor-name@instance.tld`. Actors like Persons and Groups and Applications have Public Keys attached to them, as well as their ID is probably cached by most software. So assigning some actor-name to something new also can cause unintended behavior.
-
-If multiple plugins want to individually federate their content (like events, products and blog posts or even the built-in WordPress categories), they must be able to have something like an actor API, the ActivityPub plugin can register. The ActivityPub plugin being the main coordinator is necessary because actors are globally unique. 
-- For existing (collision was created before the installation/activation of the plugin)
-- For new collisions (collision was/will be created after the installation/activation of the plugin)
-
-It seems like it is the best if collisions are avoided in the first place by encouraging the use of prefixes, like `category_<category>`.
-
-Anyway it seems the question has to be raised wheter activitypub should store a history of all past and currently mapped actors. Currently the ActivityPub plugin is still written with WordPress users being the default ActivityPub actors in mind. This also reflects in things like the class which is responsible for the actor lookup is still called `Users` and yet handles the `Blog` and the `Application` user too, see the [Source](https://github.com/Automattic/wordpress-activitypub/blob/master/includes/collection/class-users.php).
-
-### Existing collisions
-- **Easy:** Either we just tell the user to resolve all conflicts before a WordPress actor type can be activated at all
-- **Complex:** We let him choose alternatives for conflicts.
-
-### New collisions
-- **Easy** Forbid the saving of new users or posts that would conflict with an existing actor.
-- **Complex** ...
-
-## Conclusion
-- Anyway it seems the question has to be raised whether the ActivityPub plugin should store a history of all past and currently mapped actors.
-- Additionally, shouldn't the user have a detailed overview in each case if the actor management should get more complex? 
-  
-
-# Appendix
-
-## The approach of youtube-dl
-
-[youtube-dl](https://github.com/ytdl-org/youtube-dl) is solving a similar problem with "extractors" that return data to the processing-chain of youtube-dl. They provide a base class that includes useful functions for common issues e.g. automatic testing, geo-bypassing, login/cookie/header management. The most [basic extractor](https://github.com/ytdl-org/youtube-dl#adding-support-for-a-new-site) is about 40 lines of code.
-They can also chain extractors recursivly, like a extractor for mastodon videos, that gets the video from the post and returns the source of the video, that could be youtube, vimeo or anything else youtube-dl supports.

event_import.md

@@ -0,0 +1,132 @@
+---
+gitea: none
+include_toc: true
+---
+
+Status: draft. This document should be reviewed by the other main developers.
+
+# Validation/Import of remote events
+This document gives an overview how remote `Event` objects are treated by common Fediverse applications.
+
+## Mastodon
+**Last updated**: 2024-10-20
+
+Mastodon does not have support or events, but an `Event` object is in the [list of converted object types](https://github.com/mastodon/mastodon/pull/12637/commits/0428c00e30abcb0580558f9bdca672abc8b68f81).
+
+It neglets all event related fields but `title`, `summary` and `url` which it uses to create a Mastodon status (toot) representation of the event.
+
+
+## Mobilizon
+**Last uptaded**: 2024-01-20
+
+**Information sources**:
+
+- [Mobilizon ActivityStreams converter for Event](https://framagit.org/framasoft/mobilizon/-/blob/main/lib/federation/activity_stream/converter/event.ex?ref_type=heads)
+- [Mobilizon Database schema for Event](https://framagit.org/framasoft/mobilizon/-/blob/main/lib/mobilizon/event.ex?ref_type=heads)
+
+### Required
+
+- [`attributedTo`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-attributedTo) or [`actor`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-actor): Mobilizon uses actor for the user profile and attributedTo for the group. But as `actor` being part of an object is not part of the ActivityPub spec, solely using `attributedTo` might preferred if they are similar.
+- `id`: This is also used for the `url`.
+- [`name`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-name): The events title.
+- [`startTime`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-startTime)
+- [`to`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-to)
+- [`type`]: must be `Event`
+
+### Optional
+
+- [`attachment`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-attachment) How they are used
+- [`anonymousparticipationenabled`](https://docs.joinmobilizon.org/contribute/activity_pub/#anonymousparticipationenabled)
+- `category`: default list of categories can be found [in the source code](https://framagit.org/framasoft/mobilizon/-/blob/main/lib/mobilizon/events/categories.ex?ref_type=heads#L28), but it can be extended via environment variables. Note that the source code shows them in lowercase, but they have to be passed as uppercase, e.g. `MOVEMENTS_POLITICS`.
+- [`commentsEnabled`](https://docs.joinpeertube.org/api/activitypub)
+- `contacts`: a list of contacts: each item might be just the `id`/`url` or an `Actor` object.
+- [`content`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-content): `contentMap` is currently not supported by Mobilizon.
+- [`endTime`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-endTime)
+- `externalParticipationUrl`: Only used if `joinMode` is set to `external`.
+- `is_online`: Boolean indicating whether the Event is online.
+- [`joinMode`](https://docs.joinmobilizon.org/contribute/activity_pub/#joinmode): `[free, restricted, invite, external]` default is `free`.
+- [`location`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-location): The subkey [`address`](https://schema.org/address) is accepted, both as [`PostalAddress`](https://schema.org/PostalAddress) and pure text.
+- [`maximumAttendeeCapacity`](https://docs.joinmobilizon.org/contribute/activity_pub/#maximumattendeecapacity)
+- [`mentions`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-mentions)
+- `metadata`: This is a list that can contain items. TODO.
+- `participantCount`: [Not parsed at the moment](https://framagit.org/framasoft/mobilizon/-/issues/1412)
+- [`repliesModerationOption`](https://docs.joinmobilizon.org/contribute/activity_pub/#repliesModerationOption)
+- `remainingAttendeeCapacity`: [Not parsed at the moment](https://framagit.org/framasoft/mobilizon/-/issues/1412)
+- [`tag`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-tag)
+- `timezone`
+- `url`: [Documentation](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-url) - Note: `url` was added to the list as it was referenced in the text but not explicitly listed in the initial set.
+
+### Not used
+
+- [`url`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-url): internally Mobilizon uses the `id` as URL.
+
+
+### To Test:
+
+### Handling of visibility, comments and discoverability
+
+- If `https://www.w3.org/ns/activitystreams#Public` is not in `to` it will be treated as `unlisted`, else as `public`. This are the only options for remote events, even though internally Mobilizon supports `[public, unlisted, restricted, private]`.
+- For comments to be enabled within Mobilizon either [`commentsEnabled`](https://docs.joinpeertube.org/api/activitypub) must be `true` or `repliesModerationOption` must be set to `allow_all`. `repliesModerationOption` is more important. If none is of both is passed replies will be disabled.
+- When the `attributedTo` (or if `attributedTo` is not set, but `actor` is set) contains an `Actor` of type `Person` the remote `Event` will not be listed and searchable.
+- If `timezone` is not defined Mobilizon might calculate the timezone via the `location`.
+
+
+### Attachment/Banner-image handling
+
+Mobilizon currently expects all images to by within `attachment` and to be an `Object` of type `Document`. It first looks for an object where the `name` is equal to `Banner`. If that is not found it uses ´attachment[0]`.
+
+## Gancio
+
+**Last uptaded**: 2024-01-20
+
+### Required
+
+- `id`: even though Gancio currently does not [list it as required in its source code](https://framagit.org/les/gancio/-/blob/master/server/federation/events.js?ref_type=heads#L19), there will be an error without out it.
+- [`name`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-name): The events title.
+- [`startTime`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-startTime)
+
+### Optional
+
+- [`attachment`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-attachment) Only the first one is used as a banner image, all others are ignored, see below.
+- [`content`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-content) `contentMap` is currently not supported by Gancio.
+- [`endTime`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-endTime)
+- [`location`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-location): The subkey [`address`](https://schema.org/address) is accepted, both as [`PostalAddress`](https://schema.org/PostalAddress) and pure text. For `PostalAddress` only  `streetAddress`, `addressLocality`, and `addressCountry` are used.
+- [`summary`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-summary) The summary is only used when no content is supplied.
+
+### Not used
+
+- `attributedTo`/`actor`: Gancio does not support fetching event other than by receiving a `Create` or `Update` activity (TODO: what about `Announce`), the actor is always just fetched from the activity, not the object within.
+
+### Handling of visibility
+
+Currently Gancio does not seem to handle any visibility or replies-policy options. It sets all remote events it received to the internal `is_visible` to `true`.
+
+### Banner image
+
+Gancio takes the first `attachment` of the `Event` object as the banner image of the event. It optionally supports [`name`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-name) as the alternative text and [`focalPoint`](https://docs.joinmastodon.org/spec/activitypub/#focalPoint).
+
+
+## Plemora
+
+**Last uptaded**: 2024-01-20
+
+**Information sources**: Plemora has a open [Pull Request towards Mobilizon compatible events](https://git.pleroma.social/pleroma/pleroma/-/merge_requests/3955/diffs) which Rebased (a fork of Plemora) has already merged.
+
+### Required
+
+This probably has a lot of errors still. [Source Code](https://git.pleroma.social/pleroma/pleroma/-/blob/b1a06c394736be833f8220a5ec3d5d2702d9519c/lib/pleroma/web/activity_pub/object_validators/event_validator.ex).
+
+- `id`: even though Gancio currently does not [list it as required in its source code](https://framagit.org/les/gancio/-/blob/master/server/federation/events.js?ref_type=heads#L19), there will be an error without out it.
+- [`name`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-name): The events title.
+- [`startTime`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-startTime)
+- [`endTime`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-endTime)
+
+
+### Optional
+
+- [`joinMode`](https://docs.joinmobilizon.org/contribute/activity_pub/#joinmode): `[free, restricted, invite, external]` default is `free`.
+- [`location`](https://www.w3.org/TR/activitystreams-vocabulary/#dfn-location): The subkey [`address`](https://schema.org/address) is accepted, but currently ony as [`PostalAddress`](https://schema.org/PostalAddress) with the fields `postalCode`, `addressRegion`, `streetAddress`, `addressCountry` and `addressLocality`.
+
+### Handling of visibility
+
+Does not seem to be handled. 

external.md

@@ -0,0 +1,31 @@
+# External work
+
+Work done on other projects for interoperability. If the discussion is complete or a pull-request/fix is merged it is marked by [x].
+
+## Wordpress ActivityPub
+- [x] [Pull Requests: Add/event objects ](https://github.com/Automattic/wordpress-activitypub/pull/629)
+- [ ] [Pull Requests: Add/Advanced Follow Management](https://github.com/Automattic/wordpress-activitypub/pull/622)
+
+## Mobilizon
+- [x] [Improve (fix) detection of Banner Image](https://framagit.org/framasoft/mobilizon/-/merge_requests/1527/)
+
+- [x] [Review/Bugreport for FEP-2667 implementation](https://framagit.org/framasoft/mobilizon/-/merge_requests/1507#note_2037833)
+- [x] [Bugreport for relay following](https://framagit.org/framasoft/mobilizon/-/issues/1392)
+- [x] [Report on missing info about remote event visibility](https://framagit.org/framasoft/mobilizon/-/issues/1385)
+- [x] [Context for Place](https://framagit.org/framasoft/mobilizon/-/issues/1388)
+- [x] [pure text address fields](https://framagit.org/framasoft/mobilizon/-/issues/1387)
+- [x] [Bug report for ical:status not being compacted](https://framagit.org/framasoft/mobilizon/-/issues/1378)
+- [ ] Report missing context for externalParticipationUrl](https://framagit.org/framasoft/mobilizon/-/issues/1376)
+
+## Gancio
+- [x] [Issue: Summary vs content](https://framagit.org/les/gancio/-/issues/304)
+- [x] [Improve json-ld representation of events ](https://framagit.org/les/gancio/-/merge_requests/33)
+- [x] [Discussion: HTML should be supported for summary](https://framagit.org/les/gancio/-/issues/321)
+
+## Plemora
+- [x] [Review/Suggestions for the Pull request adding Mobilizon compatible objects](https://git.pleroma.social/pleroma/pleroma/-/merge_requests/3955)
+
+## Socialhub activitypub
+
+- [ ] [Discussion for Events Interoperability: Validation, minimum requirements, common extensions](https://socialhub.activitypub.rocks/t/events-interoperability-validation-minimum-requirements-common-extensions/3849/1)
+- [ ] [Instance Federation: Visibility of remote Events ](https://socialhub.activitypub.rocks/t/instance-federation-visibility-of-remote-events/3850)

ideas.md

@@ -0,0 +1,21 @@
+# Focal Point
+
+Support various focal point plugins, because on ActivityPub we have less control how images are rendered on the other side.
+
+https://docs.joinmastodon.org/spec/activitypub/#focalPoint
+
+## Image Background Focus Position
+
+https://www.wordpress-focalpoint.com/
+
+Meta field: `bg_pos_desktop`
+Value: string, e.g. `50% 50%`, like the css option [object-position](https://developer.mozilla.org/en-US/docs/Web/CSS/object-position)
+
+
+## WP Smart Crop
+
+https://www.wpsmartcrop.com/download/
+
+Meta field if enabled for this image: `_wpsmartcrop_enabled` bool
+Meta field: `_wpsmartcrop_image_focus`
+Value: array with keys `top` and `left` which are floats.