Complaining about the covering of the book (7)

I believe the answer is:

binding

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'covering of the book' is the definition.
'binding' can be an answer for 'covering' (binding is a kind of covering). I am not certain of the 'of the book' bit.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for binding that I've seen before include "Mandatory" , "work for a bookmaker" , "Obligatory" .)

I've seen this clue in the Evening Standard.

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