SetSplitStyle can be used to create the split slider between regions, the ability to dynamically set their sizes by the user.
The separator is assigned to the layout’s region by calling SetSplitStyle method, where you specify the name of the region and type of separator (kFBSplitStyle)
Type of separator may be as follows:
kFBHSplit – the bottom side of the region will be a split slider
kFBVSplit – the right side of the region will be a split slider
kFBHVSplit – right and bottom sides will be a split slider
Example of creating a split slider can be found in MCL , called Tool_SplitStyle.