Its not possible to use attribute type 'url' as alias in relation properties
Its not possible so save an item, because we have an error from compare widgetToValue and valueToWidget...
Before the problem can be solved, a new interface must be built into the core and the corresponding implementation built into tags.
MetaModels/core#904
https://github.com/MetaModels/core/compare/feature-aliasaware
There is already a corresponding branch for select
https://github.com/MetaModels/attribute_select/tree/feature-aliasaware
current: "known limitation"