WordPress at a glance
функция не описана

IXR_Server::setCallbacks() public WP 1.0

It's a method of the class: IXR_Server{}

Хуков нет.

Возвращает

Null. Ничего.

Использование

$IXR_Server = new IXR_Server();
$IXR_Server->setCallbacks();

Код IXR_Server::setCallbacks() WP 5.5.1

<?php
function setCallbacks()
{
    $this->callbacks['system.getCapabilities'] = 'this:getCapabilities';
    $this->callbacks['system.listMethods'] = 'this:listMethods';
    $this->callbacks['system.multicall'] = 'this:multiCall';
}