framework/base/Module.php
public function getUniqueId()
    {
        return $this->module ? ltrim($this->module->getUniqueId() . '/' . $this->id, '/') : $this->id;
    }
public function getUniqueId()
    {
        return $this->module ? ltrim($this->module->getUniqueId() . '/' . $this->id, '/') : $this->id;
    }
Returns an ID that uniquely identifies this module among all modules within the current application.
Note that if the module is an application, an empty string will be returned.
@return string the unique ID of the module.