User Manual
Page 112
... 1.4x E EF200-400mm f/4L IS USM Extender 1.4x: Built-in Ext.1.4x used F EF200-400mm f/4L IS USM Extender 1.4x + Extender EF1.4x I/II/III F EF200-400mm f/4L IS USM Extender 1.4x: Built-in Ext.1.4x used + Extender EF1.4x I /II/III) is not possible. When using a lens and Extender EF1.4x III/EF2x III in a combination marked with AF.
... 1.4x E EF200-400mm f/4L IS USM Extender 1.4x: Built-in Ext.1.4x used F EF200-400mm f/4L IS USM Extender 1.4x + Extender EF1.4x I/II/III F EF200-400mm f/4L IS USM Extender 1.4x: Built-in Ext.1.4x used + Extender EF1.4x I /II/III) is not possible. When using a lens and Extender EF1.4x III/EF2x III in a combination marked with AF.