Neos\Flow\Core\Booting\Sequence::invokeStep PHP Method

    protected function invokeStep(Step $step, Bootstrap $bootstrap)
    {
        $bootstrap->getSignalSlotDispatcher()->dispatch(__CLASS__, 'beforeInvokeStep', [$step, $this->identifier]);
        $identifier = $step->getIdentifier();
        $step($bootstrap);
        $bootstrap->getSignalSlotDispatcher()->dispatch(__CLASS__, 'afterInvokeStep', [$step, $this->identifier]);
        if (isset($this->steps[$identifier])) {
            foreach ($this->steps[$identifier] as $followingStep) {
                $this->invokeStep($followingStep, $bootstrap);
            }
        }
    }