DTDs don't have ID or IDREF elements so why does XML Schema?

[Roger L Costello <costello@mitre.org>]

Hi Folks,

DTD only allows attributes to be of type ID and IDREF.

XML Schema allows both attributes and elements to be of type ID and IDREF. Why? Is there a compelling use case for declaring an element to be of type ID? Is there a compelling use case for declaring an element to be of type IDREF?

/Roger