Stairs to attic? Excellent (3-6)
I believe the answer is:
top-flight
'excellent' is the definition.
(I've seen this before)
'stairs to attic?' is the wordplay.
'stairs' becomes 'flight' (flight is a kind of stairs).
'to' says to put letters next to each other (I've seen this in other clues).
'attic?' becomes 'top' (I can't explain this - if you can you should believe this answer much more).
'flight' put after 'top' is 'TOP-FLIGHT'.
Can you help me to learn more?
(Other definitions for top-flight that I've seen before include "Superior" , "Of the highest class" , "Highest level" , "Excellent -- best possible" .)