With re-write required, bill panto writer (9)

I believe the answer is:

ballpoint

I'm a little stuck... Click here to teach me more about this clue!

'writer' is the definition.
(I've seen this before)

'with re-write required bill panto' is the wordplay.
'bill panto' can be anagrammed to 'BALLPOINT'.
But, I'm not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for ballpoint that I've seen before include "Writer" , "Biro" , "Type of pen" .)

I've seen this clue in The Independent.

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