If you use the API to access the front panel items from an external application (which is common practice at my work place, and which if we didn't do this we would have been unable to supply the necessary functionality to our user community for the last 10 years) then this tab order is the list order that the items appear in, control or indicator, which can help in prioritising in similar situations, so whilst it may not allow for a difference in user tabbing, it can prove very helpful to list the indicators in other situations.
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