Are even in the right enclosure and that doesn't often happen (4,5)

I believe the answer is:

rare event

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'enclosure and that doesn't often happen' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'are even in the right' is the wordplay.
'in' is an insertion indicator.
'the right' becomes 'rt'.
'are'+'even'='areeven'
'areeven' put within 'rt' is 'RARE EVENT'.

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