[docs] Update output documentation for react

docs/apis/core/htmlwriter/index.md

@@ -49,6 +49,53 @@ 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.
+
+The method writes:
+
+- `data-react-component` with the module name;
+- `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 any 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
+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="{\"filter\":\"latest\",\"limit\":\"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