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ExternalResourceLoadContext.GetCurrentlyLoadedReference

Method
Description:
Returns a copy of the ExternalResourceReference currently in use by the containing element.
Remarks:

A server may use to wish this information to, for example, tell whether the Revit user was previously using their server or not.

This reference may be null if there is no current value. For example, a newly-created link being loaded for the first time would have no currently-loaded reference.