Firebase documents in Custom Code

I am passing a list of Documents to my custom widget. What is the difference between passing Documents and DocumentReferences? The generated code is always

List<XRecord>

regardless of whether I specify Document or DocumentReference in the list of parameters.

I want to loop over a list of Documents and then access another Firebase Document, which is referenced from the respective current Document I am looking at (each of the Documents passed via the parameter has a reference to another Collection).

After getting the referenced Document, I want to access its title.