Style of arrangement (6)
I believe the answer is:
format
'style of arrangement' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for format that I've seen before include "Way of presentation" , "Secure firmly in position" , "Prepare (a disk) for data" , "The shape and size, of a book say" , "Style or arrangement of a TV programme" .)