Helper variable that contains the value of the third user information field on the predefined RegistrationDlg dialog box; it is typically used for the product's registration key. This information is entered by the user and is optionally stored in the registry by the installer (as controlled by the options on the User interface project page).
You can refer to this variable as <UserField3>. By default this variable is set to an empty value. However, you can initialize this variable to any suitable value. You can also use a Set Variable action to change its value at installation time.