<type name="Magento\Framework\View\Layout\PageType\Config\Reader">
    <arguments>
        <argument name="fileName" xsi:type="string">
            page_types.xml
        </argument>
        <argument name="converter" xsi:type="object">
            Magento\Framework\View\Layout\PageType\Config\Converter
        </argument>
        <argument name="schemaLocator" xsi:type="object">
            Magento\Framework\View\Layout\PageType\Config\SchemaLocator
        </argument>
        <argument name="defaultScope" xsi:type="string">
            frontend
        </argument>
    </arguments>
</type>

This is a type configuration.

This configuration is the application level configuration (`app/etc/di.xml`) fo the object manager. It is not a part of a specific module, but will apply to all sub-applications in Magento 2 (cart, admin, api, cron, etc).

This configuration tells the Object Manager that when a user wants a Magento\Framework\View\Layout\PageType\Config\Reader object that the following arguments should be used in the foo object's constructor.

• $fileName = "page_types.xml";
• $converter = new Magento\Framework\View\Layout\PageType\Config\Converter (...)
• $schemaLocator = new Magento\Framework\View\Layout\PageType\Config\SchemaLocator (...)
• $defaultScope = "frontend";

<virtualType name="Magento\Framework\View\Layout\PageType\Config\Data"
             type="Magento\Framework\Config\Data">
    <arguments>
        <argument name="reader" xsi:type="object">
            Magento\Framework\View\Layout\PageType\Config\Reader
        </argument>
        <argument name="cacheId" xsi:type="string">
            page_types_config
        </argument>
    </arguments>
</virtualType>

This is a virtual type configuration.

This configuration is the application level configuration (`app/etc/di.xml`) fo the object manager. It is not a part of a specific module, but will apply to all sub-applications in Magento 2 (cart, admin, api, cron, etc).

This virtualType configuration tells the Object Manager when a user wants a virtual Magento\Framework\View\Layout\PageType\Config\Data object that it should return a Magento\Framework\Config\Data object.

This configuration tells the Object Manager that when a user wants a Magento\Framework\View\Layout\PageType\Config\Data object that the following arguments should be used in the foo object's constructor.

• $reader = new Magento\Framework\View\Layout\PageType\Config\Reader (...)
• $cacheId = "page_types_config";