sourceActorInRole- type attribute needed
http://balilabs.de/rr/edlido.html?e=Beispielschnipsel_attribution.xml
In order to give a hint, whether the source is an uri or just a text (whether printed or not), shall we introduce a type attribute for any kind of source element? (not sure)
Might also be relevant for: sourceRelatedWorkSet/sourceAppellation/sourceRepositorySet/sourceDescriptiveNote/sourceMaterialsTech