XACT_EVENT for 'commit prepared'

I found that in enum XactEvent, there is  'XACT_EVENT_PREPARE'  for 'prepare transaction', but there is no event for 'commit prepared' or 'rollback prepared'.

For the following SQL:

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begin;

create table test(a int);

PREPARE TRANSACTION 'foo';

rollback prepared 'foo';

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When executing ' rollback prepared 'foo'; ', I expected to get 'XACT_EVENT_ABORT', but actually, 

the event type is 'XACT_EVENT_COMMIT'. 

I think XACT_EVENT_COMMIT_PREPARED and XACT_EVENT_ROLLBACK_PREPARED can be added in function 'FinishPreparedTransaction'

I'm confused why there are no related events for them.