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1b1ed1a
(Get the code!)
I agree this should be documented.
Here is a proposed text:
In almost all cases a PRIMARY KEY or UNIQUE INDEX needs to be present in the table. This is necessary because the tool creates a DELETE trigger to keep the new table updated while the process is running.
A notable exception is when a PRIMARY or UNIQUE index is being created from existing columns as part of the ALTER clause; in that case it will use these column(s) for the DELETE trigger.