The TBN_BEGINADJUST notification message notifies a toolbar’s parent window
that the user has begun customizing a toolbar. This message is sent in the
form of a WM_NOTIFY message.
TBN_BEGINADJUST
pnmhdr = (NMHDR FAR *) lParam;
Parameters
pnmhdr
Pointer to an NMHDR structure that contains information about the
notification message.