Would modified carols fit into special glasses? (9)

I believe the answer is:

trifocals

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

'special glasses?' is the definition.
(I've seen this before)

'would modified carols fit' is the wordplay.
'carols fit' anagrams to 'TRIFOCALS'.
However, I'm not sure how this is indicated.

'into' acts as a link.

Can you help me to learn more?

(Other definitions for trifocals that I've seen before include "Spectacles" , "Special glasses" .)

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

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