Windows 10 Rotation

Control-Alt-Left   - anticlockwise rotation 90 degrees
Control-Alt-Right   - clockwise rotation 90 degrees
Control-Alt-Up - upright
Control-Alt-Down - upside down

System.Windows.Forms.Splitter

This Windows Forms Splitter control is a legacy component and has been replaced by the SplitContainer class. It can be safely ignored except for compatibility reasons. The SplitContainer is more intuitive to use than Splitter.