NSIS_CONFIG_LOG how and where to define?

[micahel]

Hi,

I have another question regarding the logging. The docs say:

4.9.12.1 LogSet
on|off
Sets whether install logging to $INSTDIR\install.log will happen. $INSTDIR must have a value before you call this function or it will not work. Note that NSIS_CONFIG_LOG must be set in the installer configuration (it is not by default) to support this.

Here my question:
How can I set the NSIS_CONFIG_LOG ?
Where shall I set it ? In the script file of MY installer-script or in the config files of NSIS?

Thanks
Michael