feat(corrections): add corrections and clarifications behind feature flag

includes/class-newspack.php

@@ -125,6 +125,7 @@ private function includes() {
 		include_once NEWSPACK_ABSPATH . 'includes/tracking/class-twitter-pixel.php';
 		include_once NEWSPACK_ABSPATH . 'includes/revisions-control/class-revisions-control.php';
 		include_once NEWSPACK_ABSPATH . 'includes/authors/class-authors-custom-fields.php';
+		include_once NEWSPACK_ABSPATH . 'includes/corrections/class-corrections.php';
 
 		include_once NEWSPACK_ABSPATH . 'includes/starter_content/class-starter-content-provider.php';
 		include_once NEWSPACK_ABSPATH . 'includes/starter_content/class-starter-content-generated.php';

includes/corrections/README.md

@@ -0,0 +1,34 @@
+# Corrections
+
+This feature allows authors to add article corrections to the top or bottom of a post.
+
+## How it works
+
+When you enable this feature, a new meta box will be added to the post editor screen. You can use this meta box to add a correction to the post. The correction will be displayed at the top or bottom of the post, depending on the settings.
+
+## Usage
+
+This feature can be enabled by adding the following constant to your `wp-config.php`:
+
+```php
+define( 'NEWSPACK_CORRECTIONS_ENABLED', true );
+```
+
+## Data
+
+Corrections are stored as `newspack_correction` custom post type. A correction consists of the following fields:
+
+| Name                          | Type     | Stored As      | Description                                                     |
+| ----------------------------- | -------- | -------------- | --------------------------------------------------------------- |
+| `title`                       | `string` | `post_title`   | The correction title. Defaults to 'Correction for [post title]' |
+| `content`                     | `string` | `post_content` | The correction text.                                            |
+| `date`                        | `string` | `post_date`    | The date assigned to the correction.                            |
+| `newspack_correction-post-id` | `int`    | `post_meta`    | The ID of the post to which the correction is associated.       |
+
+In addition, some correction data is stored in the associated post as post meta:
+
+| Name                            | Type                    | Stored As   | Description                                                   |
+| ------------------------------- | ----------------------- | ----------- | ------------------------------------------------------------- |
+| `newspack_corrections_active`   | `bool`                  | `post_meta` | Whether the feature is enabled for the post.                  |
+| `newspack_corrections_location` | `string`                | `post_meta` | Where the correction should be displayed. (`top` or `bottom`) |
+| `newspack_corrections_ids`      | `array`                 | `post_meta` | An array of IDs of the corrections associated with the post.  |