EN_KILLFOCUS
idEditControl = LOWORD(wParam);
hwndEditControl = (HWND)lParam;
The EN_KILLFOCUS notification message is sent when an edit control loses the input focus. The control's parent window receives this notification message through a WM_COMMAND message.
idEditControl
Value of low word of wParam. Specifies the edit-control ID.
hwndEditControl
Value of lParam. Specifies the edit-control window handle.
WM_COMMAND