Allow foreign attributes and elements in LIDO
Link to DDB Wiki for further information: TBD
Use case: For some application profile it is useful to augment certain LIDO elements with their own attributes and/pr elements, i.e. nodes with a non-LIDO namespace. This comes in handy e.g. for automatically enrich data with information from authority files. However, inserting foreign nodes isn't valid in the current schema.
Note: Similar to allowing SKOS in certain contexts.