A container that accepts only two child controls, then arranges them vertically and creates a divisor between them. The divisor can be dragged around to change the size relation between the child controls.
Boolean value. If 1 ([code]true[/code]), the grabber will hide automatically when it isn't under the cursor. If 0 ([code]false[/code]), it's always visible.
The minimum thickness of the area users can click on to grab the splitting line. If [theme_item separation] or [theme_item grabber]'s thickness are too small, this ensure that the splitting line can still be dragged.