If this function returns a non-NULL string, it means that the this requires you to specify product registration key through InstallConfig instance passed to script generation methods.

The returned string specifies the expected format of the product key like this:

@ - any character % - alphabet

- numeric character

$ - alphanumeric character

All other characters represent themselves.

For example in case of installer for Microsoft Windows XP, you'll get "$$$$$-$$$$$-$$$$$-$$$$$-$$$$$". That means a product key consists of 24 alphanumeric characters and 4 '-' characters at (0-based) indices 5, 11, 17 and 23.

Parameters:

this	the install script

Returns:

Product key format mask, or NULL.