Extremist papers served up the same thing (5)
I believe the answer is:
ditto
'the same thing' is the definition.
(the thing previously mentioned in a list)
'extremist papers served up' is the wordplay.
'extremist' becomes 'ott' (I can't justify this - if you can you should believe this answer much more).
'papers' becomes 'ID' (identifying documents are one's 'papers').
'served up' says the letters should be written in reverse (in a down clue, going upwards).
'ott'+'id'='ottid'
'ottid' written backwards gives 'DITTO'.
Can you help me to learn more?
(Other definitions for ditto that I've seen before include "that which has been said" , "Two dots say same again" , "Do alternative" , "Dot it for the same again" , "The same thing" .)