A developing area (8)
I believe the answer is:
darkroom
'a developing area' is the definition.
(I've seen this before)
'a developing area' is the wordplay.
'a developing' becomes 'dark' (I can't justify this - if you can you should believe this answer much more).
'area' becomes 'room' (room is a kind of area).
'dark'+'room'='DARKROOM'
Can you help me to learn more?
(Other definitions for darkroom that I've seen before include "development area" , "Film developer's workplace" , "In which to develop photographs" , "Place to develop films" , "Place for developing photographs" .)