How is `event_data` supposed to work?

Let's say we have the CONTENT_OBJECT_ASSOCIATIONS_CHANGED event:

https://github.com/openedx/openedx-events/blob/34d3fce371f14c892d77284f9fcba8a5e67fc544/openedx_events/content_authoring/signals.py#L239-L249

And I want to add the context (course/library ID) to this event, like this:

  CONTENT_OBJECT_ASSOCIATIONS_CHANGED = OpenEdxPublicSignal( 
      event_type="org.openedx.content_authoring.content.object.associations.changed.v1", 
      data={ 
          "content_object": ContentObjectChangedData,
+         "context": ContextIdData,
      } 
  ) 

Is that sort of change allowed? If so, how would I update event_data in the comment/documentation of the event? If not, why is data a dictionary? How do we know from the in-line code annotation what key (e.g. content_object) the event data is under?

This is not explained in the docs as far as I can see.

Start with openedx_events/content_authoring/signals.py at the CONTENT_OBJECT_ASSOCIATIONS_CHANGED definition, then read the linked inline-code-annotations documentation. Review the comment thread for the intended event_data and data-key behavior, and update the documentation so the mapping and allowed context field are explicit; done means the original questions can be answered from the docs.