In Magento 2, when you add a menu item, you need to specify a module
attribute (module="Magento_Backend"
below)
<add id="Magento_Backend::system_currency"
title="Currency"
module="Magento_Backend"
sortOrder="30"
parent="Magento_Backend::stores"
action="adminhtml/system_currency"
resource="Magento_CurrencySymbol::system_currency"
/>
What does the Magento system use this attribute for? i.e., why does the menu rendering need to know which module a Menu Item comes from?