That's a good question. I haven't implemented this option, and there is an merge request to remove that option again, which has been merged already: !21 (merged)
For some reason this command line option has survived. However, it is not evaluated anymore. We should remove it entirely.
I know. But I thought that this option was actually reverted in !21 (merged) , so it would be better to remove an unused option, rather than updating its documentation.
However, it turned out that !21 (merged) reverted only a small issue, not the whole command line option. Hence, I have deleted the branch that was deleting this option. Now I have assigned Tiago to do what you actually asked for: update the documentation.
Maybe you commented on the pull !47 (closed) which is weirdly closed. Anyways, this issue is about updating its documentation and nobody wants this feature removed.
I have closed !47 (closed) since I realized that I cannot remove the environment variable as it was not unused. I have also removed the source branch, as it was not working anyways.