The id of the feature: its properties.id, else its top-level id — the id the
module's getShown() and event handlers hand back. Cannot be used together with index.
The zero-based position of the feature in the collection the module's getShown()
returns for it. Where a module draws its features in several sources, each source counts
its own. Cannot be used together with id.
Parameters to identify a shown feature by its ID or by its index.