A request for a technical change to the XML Schema: Add si:unitType as an XML type for units

In the XML Schema version 1.2.0, which corresponds to the EMPI SmartCom data model version 1.2, the XML type for the <si:unit> elements is xs:string. For clarity and forward compatibility, it would be good to change this type to a new, separate, explicit style. It is suggested that the type name would be si:unitType.

The corresponding merge request and some more technical discussion can be found here: https://gitlab1.ptb.de/d-ptb/d-si/xsd-d-si/merge_requests/3

As discussed in the merge request, disallowing white space from <si:unit> elements might be a good next step, perhaps to be implemented in the same change request.