UXSplitDivider

UXSplitDivider is the divider of a UXSplitView. It has two sizes. Its bounds are a wide grab band, because a thin one is too hard to hit. It paints only the hairline seam at its centre, because the panes abut underneath and the Cocoa look is a line, not a bar. It is drawn last, so it wins the hit test.

A press calls the split view’s beginDragDivider, which waits in the driver’s modal trackDragStep and re-lays the panes live on each step.

The split view constructs and wires one in attachTo; nothing else does.