Suppose a job contains 3 maintenance tasks. It would be nice (a) to be able to specify the execution order of the tasks; (b) on adding a fourth task, to be able to specify where in the execution sequence it should go. (If this feature is already present, I have not found it yet).

Yes, it is present. Open the Job and go to the Task tab. You can change the order there. By default, all Tasks run in order.

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Thanks. Surprisingly, that control was a little hard to find. Maybe, in the new version, instead of a spinner on the right of the toolbar, two icon-buttons on the left, over the "Order" Column: "<uparrow> Move Up", "<Downarrow> Move down". Or just "Order <spinner>" directly above the "Order" column.