Obvious information to be included in design (5)
I believe the answer is:
plain
'obvious' is the definition.
(similar in meaning)
'information to be included in design' is the wordplay.
'information' becomes 'pain' (pain is a kind of information).
'to be included' indicates putting letters inside.
'in design' becomes 'l' (I can't explain this - if you can you should believe this answer much more).
'pain' going around 'l' is 'PLAIN'.
Can you help me to learn more?
(Other definitions for plain that I've seen before include "Undecorated; clear" , "open country" , "ugly" , "Flat land; unmarked" , "Not complicated" .)