Central parts of Madrid liable to be quite boring (4)

I believe the answer is:

drab

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'quite boring' is the definition.
'drab' can be an answer for 'boring' (I've seen this in another clue). I am unsure of the 'quite' bit.

'central parts of madrid liable to' is the wordplay.
'central parts of' says to take the centre.
'liable to' becomes 'ab' (I can't justify this - if you can you should give a lot more credence to this answer).
The middle of 'madrid' is 'dr'.
'dr'+'ab'='DRAB'

'be' acts as a link.

Can you help me to learn more?

(Other definitions for drab that I've seen before include "Colourless kind of bard" , "Colourless like bard" , "Lacklustre" , "Sombre" , "woman with slatternly habits" .)

I've seen this clue in The Irish Times.

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