Drug prosecution is the stuff of headlines? (5-4)

I believe the answer is:

upper-case

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'of headlines?' is the definition.
The definition suggests a singular noun which matches the answer.

'drug prosecution is the stuff' is the wordplay.
'drug' becomes 'upper' (a type of stimulating drug).
'prosecution' becomes 'cas' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'is the' becomes 'definitearticle' ('the' is the definite article in English).
'stuff' says to take the centre (I've seen 'stuffing' mean this).
The middle letter of 'definitearticle' is 'e'.
'upper'+'cas'+'e'='UPPER-CASE'

Can you help me to learn more?

(Other definitions for upper-case that I've seen before include "In capitals" , "Capital" .)

I've seen this clue in The Independent.

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