[docs] Update output documentation for react

docs/apis/core/htmlwriter/index.md

@@ -49,6 +49,61 @@ html_writer::start_span('zombie') . 'BRAINS' . html_writer::end_span();
 // <span class="zombie">BRAINS</span>
 ```
 
+### react_component {/* #react-component */}
+
+<Since issueNumber="MDL-89296" version="5.3" />
+
+```php
+html_writer::react_component(
+    string $modulename,
+    array|string|\stdClass|\JsonSerializable $props,
+);
+```
+
+Render a placeholder `<div>` for a React component mount point.
+
+:::note[Properties]
+
+The `$modulename` must include the `@moodle/lms/` prefix in the module name.
+
+The `$props` takes the data and JSON-encodes it. You should not pass a JSON-encoded value.
+
+:::
+
+The method outputs the `<div>` with two data attributes:
+
+- `data-react-component` with the module name, including the full `@moodle/lms/` prefix;
+- `data-react-props` containing JSON-encoded props.
+
+:::caution[A note on React properties]
+
+For React components we **strongly** encourage you to limit the properties to only the initial configuration and preferences.
+
+React properties **should not** contain additional data.
+
+Historically it was often necessary to include a range of additional properties when writing Mustache template context properties because of limitations in the way that Mustache works. For example it was often necessary to provide certain strings, as well as some hard-to-fetch data. These limitations are not present in React.
+
+:::
+
+Example usage:
+
+```php
+echo html_writer::react_component(
+    '@moodle/lms/core/example',
+    (object) [
+        'filter' => get_user_preference('tool_demo/widget_filter', 'all'),
+        'limit' => get_user_preference('tool_demo/widget_result_limit', 25),
+    ],
+);
+// <div data-react-component="@moodle/lms/core/example" data-react-props="{&quot;filter&quot;:&quot;latest&quot;,&quot;limit&quot;:25}"></div>
+```
+
+:::note
+
+If you are rendering a `\core\output\react_component_renderable` via `renderer_base::render()`, Moodle calls this method for you.
+
+:::
+
 ### Generic tags {/* #generic-tags */}
 
 ```php