Button hats over hair (4,4)

I believe the answer is:

caps lock

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

'button' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'hats over hair' is the wordplay.
'hats' becomes 'caps' (cap is a type of hat).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'hair' becomes 'lock' (lock is a kind of hair).
'caps'+'lock'='CAPS LOCK'

Can you help me to learn more?

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

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