<type name="Magento\Framework\EntityManager\Operation\AttributePool">
    <arguments>
        <argument name="extensionActions" xsi:type="array">
            <item name="eav" xsi:type="array">
                <item name="default" xsi:type="array">
                    <item name="read" xsi:type="string">
                        Magento\Eav\Model\ResourceModel\ReadHandler
                    </item>
                    <item name="create" xsi:type="string">
                        Magento\Eav\Model\ResourceModel\CreateHandler
                    </item>
                    <item name="update" xsi:type="string">
                        Magento\Eav\Model\ResourceModel\UpdateHandler
                    </item>
                </item>
            </item>
        </argument>
    </arguments>
</type>

This is a type configuration.

This configuration is for the base area. Base area configurations will apply to all the sub-applications.

This configuration tells the Object Manager that when a user wants a Magento\Framework\EntityManager\Operation\AttributePool object that the following arguments should be used in the foo object's constructor.

• $extensionActions = [...items...];

<virtualType name="Magento\Catalog\Model\ResourceModel\CreateHandler"
             type="Magento\Eav\Model\ResourceModel\CreateHandler">
    <arguments>
        <argument name="metadataPool" xsi:type="object">
            Magento\Catalog\EntityCreator\MetadataPool
        </argument>
        <argument name="scopeResolver" xsi:type="object">
            Magento\Catalog\Model\Entity\CreationScopeResolver
        </argument>
    </arguments>
</virtualType>

This is a virtual type configuration.

This configuration is for the base area. Base area configurations will apply to all the sub-applications.

This virtualType configuration tells the Object Manager when a user wants a virtual Magento\Catalog\Model\ResourceModel\CreateHandler object that it should return a Magento\Eav\Model\ResourceModel\CreateHandler object.

This configuration tells the Object Manager that when a user wants a Magento\Catalog\Model\ResourceModel\CreateHandler object that the following arguments should be used in the foo object's constructor.

• $metadataPool = new Magento\Catalog\EntityCreator\MetadataPool (...)
• $scopeResolver = new Magento\Catalog\Model\Entity\CreationScopeResolver (...)