The user can select, delete, or move text in an edit control. Windows maintains an internal flag for each edit control indicating whether the content of the control has been modified. Windows clears this flag when it creates the control and sets the flag whenever the text in the control is modified. You can retrieve the modification flag by sending the control an EM_GETMODIFY message and set or clear the modification flag by sending the control an EM_SETMODIFY message. These messages apply to both single-line and multiline edit controls.