framework/base/Module.php
public function has($id, $checkInstance = false)
    {
        return parent::has($id, $checkInstance) || (isset($this->module) && $this->module->has($id, $checkInstance));
    }
public function has($id, $checkInstance = false)
    {
        return parent::has($id, $checkInstance) || (isset($this->module) && $this->module->has($id, $checkInstance));
    }
{@inheritdoc}

Since version 2.0.13, if a component isn't defined in the module, it will be looked up in the parent module.
The parent module may be the application.