An application sends a ZGM_GETEDITTEXT to get the text of a cell's edit box after the edit is finished, but before the text is stored in the cell.
ZGM_GETEDITTEXT
wParam = (WPARAM)(int) iChars; //length of string supplied in lParam
lParam = (LPARAM) lpszString; //pointer to string to retrieve edit text
This message does not return a value.