The container control sends a WM_CONTROL (in Container Controls) message with the CN_REALLOCPSZ notification code to its owner whenever container text is edited. It is sent before the CN_ENDEDIT notification code is sent.

param1
     USHORT        id             /*  Container control ID. */
     USHORT        CN_REALLOCPSZ  /*  Notification code. */

param2
     PCNREDITDATA  pCnrEditData   /*  Pointer to the CNREDITDATA structure. */