Keeps sealing manila envelope for layouts (7)

I believe the answer is:

formats

I'm a little stuck... Click here to teach me more about this clue!

'layouts' is the definition.
(I've seen this in another clue)

'keeps sealing manila envelope' is the wordplay.
'keeps' becomes 'forts'.
'sealing' is an insertion indicator (inserted letters are sealed inside).
'manila envelope' becomes 'ma' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'forts' placed around 'ma' is 'FORMATS'.

'for' is the link.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

Want a hint initially instead of a full solution? Install my app