Form of writing regularly seen in Shanghai (4)
I believe the answer is:
saga
'form of writing' is the definition.
(type of written work)
'regularly seen in shanghai' is the wordplay.
'regularly seen in' means one should take alternating letters.
The alternating letters of 'shanghai' are 'SAGA'.
(Other definitions for saga that I've seen before include "Epic - legend" , "Norse epic" , "Flag associated with a" , "Norse narrative" , "Soap opera" .)