Let me illustrate my question with a particular (naive) example of a list.
sage: a=graphs.CompleteGraph(3)
sage: b=graphs.CompleteGraph(4)
sage: c=[a,b]
In this situation if in a new line one writes down "a." and press "Tab", then one gets a list of all options to be used for the object a (for example "a.category", "a.center", etc.).
On the other hand, if in a new line one writes down "c[0]." and press "Tab", then one does not get the right feedback. Is there some way to make this work like in the previous paragraph (and display the options for the object "c[0]"?