An open-and-shut case for the viewer? (6)
I believe the answer is:
eyelid
'an open-and-shut' is the definition.
I can't tell whether this defines the answer.
'case for the viewer?' is the wordplay.
'case' becomes 'lid' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'the viewer?' becomes 'eye' (organ which sees or views).
'lid' after 'eye' is 'EYELID'.
Can you help me to learn more?
(Other definitions for eyelid that I've seen before include "One winks with it" , "It's used in blinking" , "Natural optic protector" , "Fold of skin on the face" , "Optic membrane" .)