WP_REST_Revisions_Controller::get_item PHP Method

    public function get_item($request)
    {
        $parent = get_post($request['parent']);
        if (!$request['parent'] || !$parent || $this->parent_post_type !== $parent->post_type) {
            return new WP_Error('rest_post_invalid_parent', __('Invalid post parent ID.'), array('status' => 404));
        }
        $revision = get_post($request['id']);
        if (!$revision || 'revision' !== $revision->post_type) {
            return new WP_Error('rest_post_invalid_id', __('Invalid revision ID.'), array('status' => 404));
        }
        $response = $this->prepare_item_for_response($revision, $request);
        return rest_ensure_response($response);
    }