+ * @param string|array $args {
+ * Optional. An array or string of XML response arguments.
+ *
+ * @type string $what XML-RPC response type. Used as a child element of `<response>`.
+ * Default 'object' (`<object>`).
+ * @type string|false $action Value to use for the `action` attribute in `<response>`. Will be
+ * appended with `_$id` on output. If false, `$action` will default to
+ * the value of `$_POST['action']`. Default false.
+ * @type int|WP_Error $id The response ID, used as the response type `id` attribute. Also
+ * accepts a `WP_Error` object if the ID does not exist. Default 0.
+ * @type int|false $old_id The previous response ID. Used as the value for the response type
+ * `old_id` attribute. False hides the attribute. Default false.
+ * @type string $position Value of the response type `position` attribute. Accepts 1 (bottom),
+ * -1 (top), html ID (after), or -html ID (before). Default 1 (bottom).
+ * @type string|WP_Error $data The response content/message. Also accepts a WP_Error object if the
+ * ID does not exist. Default empty.
+ * @type array $supplemental An array of extra strings that will be output within a `<supplemental>`
+ * element as CDATA. Default empty array.
+ * }