The toolbar does this.
For the rest there is no rule how it shall be added (aside from text set to text gadgets etc). Windows / Linux are not as "stupid" as OSX which enforces a given standard like "buttons can't waste space with nothing around text" and the like ...
But BM has an auto layouting. But a little different: The initial adding is your stuff to do. but afterwards you can set that all gadgets keep the relations between each other "alive" so it always looks the same. (you can force it to keep a distance constant instead of the relative distances). To use that, you use SetGadgetLayout
For the rest there is no rule how it shall be added (aside from text set to text gadgets etc). Windows / Linux are not as "stupid" as OSX which enforces a given standard like "buttons can't waste space with nothing around text" and the like ...
But BM has an auto layouting. But a little different: The initial adding is your stuff to do. but afterwards you can set that all gadgets keep the relations between each other "alive" so it always looks the same. (you can force it to keep a distance constant instead of the relative distances). To use that, you use SetGadgetLayout