EN_UPDATE
idEditControl = LOWORD(wParam);
hwndEditControl = (HWND)lParam;
The EN_UPDATE notification message is sent when an edit control is about to display altered text. This notification is sent after the control has formatted the text but before it screens the text. This makes it possible to alter the window size, if necessary. 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