[MSDN Library June 1998] WM_MDIGETACTIVE (55.7313892840209%)

MSDN Library Visual Studio 6.0 > Platform SDK > User Interface Services > Windowing > Multiple Document Interface > Multiple Document Interface Reference > MDI Messages

[MSDN Library April 2000] WM_MDIGETACTIVE (44.6202781729098%)

MSDN Library - April 2000 > Platform SDK > User Interface Services > Windows User Interface > Windowing > Multiple Document Interface > Multiple Document Interface Reference > Multiple Document Interface Messages