BCGControlBar Pro for MFC
UINT BCGM_ON_MOVE_TAB

This message is sent to the parent of tabbed window when a tab has been moved (dragged) to a new position.

Parameters
wParamspecifies the zero-based index of the tab before drag.
lParamspecifies the zero-based index of the tab after drag.
Returns
should return zero.

Process this message to be notified about tab dragging.