[DirectX 7 Programmer's Reference] Focus and Device Windows (98.9583333333333%)

Microsoft DirectX 7.0 > DirectDraw > DirectDraw Essentials > Multiple-Monitor Systems

[DirectX 5 Programmer's Reference] Focus and Device Windows (84.375%)

DirectX Foundation > DirectDraw > DirectDraw Essentials > Multiple Monitor Systems (New for Windows 98 and Windows NT 5.0)