Azure resource list expand parameter accepted values are not documented

Could you add some documentation including examples around what the expand parameter accepts in the
"/subscriptions/{subscriptionId}/resourceGroups/{resourceGroupName}/resources" GET call?

azure-rest-api-specs/specification/resources/resource-manager/Microsoft.Resources/stable/2017-05-10/resources.json

I have been considering it for getting selected VMs and their properties, and wanted to know if the expand parameter takes a similar option as the VM API's list takes. But with the given documentation I am not able to figure anything out.

Can anyone respond and also improve the documentation?