Crossword Genius

Completely riveted, in short, by composition (5,3)

Ross

I believe the answer is:

every bit

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'completely' is the definition.
I know nothing about this answer so I can't tell whether this works.

'riveted in short by composition' is the wordplay.
'in short' means to remove the last letter.
'composition' is an anagram indicator.
'riveted' with its last letter taken off is 'rivete'.
'rivete'+'by'='riveteby'
'riveteby' is an anagram of 'EVERY BIT'.

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I've seen this clue in The Irish Times.
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