nested properties

I'm querying the search API through Postman with the includefields parameter and have a question that I could not find docs for: 

How do I target nested properties? I'd like to return the author displayname from content > createdbyuser > displayname. The following query does not seem to be correct: 


"PageSize": 1, 
"PageIndex": 0, 
"TotalCount": 75, 
"SearchResults": [ 

"Url": "https://mysite/group/b/blog/posts/post", 
"Content": { 
"Url": "https://mysite/group/b/blog/posts/post

"FieldFacets": [], 
"DateRangeFacets": [], 
"Info": [], 
"Warnings": [], 
"Errors": []