Party poster contains some mistakes (5)

I believe the answer is:

typos

'some mistakes' is the definition.
(typo is a kind of mistake)

'party poster contains' is the wordplay.
'contains' indicates a hidden word.
'TYPOS' can be found hidden inside 'party poster'.

(Other definitions for typos that I've seen before include "Mistakes" , "Printing errors" .)

I've seen this clue in The Irish Times.

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