[MSDN Library June 1998] WM_MDIGETACTIVE (35.3681566181566%)

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 (34.6737121737122%)

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