the purpose of a bracket order is as follows:
- A mainside order: Basically the set price you want to enter in, could be Limit Price or StopLimit order
- A lowside order: basically an order to make sure you get out a trade in the event it goes against your initial analysis
- A highside order: When you enter, you want to make sure that you get out in time, given the trade goes in the favorable decision
All in all, it's not magic how these get executed, its all depends on which order gets hit first when you enter with your mainside order.