Part of the musical fabric? (3)

I believe the answer is:

rag

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'fabric?' is the definition.
(rag is a kind of fabric)

I don't understand how the remainder of the clue works.

(Other definitions for rag that I've seen before include "Small piece of cloth and university week" , "A tattered cloth or university frolic" , "Disreputable newspaper" , "Scott Joplin composition, for example" , "students' excuse to misbehave?" .)

I've seen this clue in the Evening Standard.

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