Where does the uplift tree n_reg regularization come from?

[brrm]

I was wondering where exactly the n_reg regularization parameter (in the UpliftTreeClassifier and UpliftRandomForestClassifier classes) was defined?
The documentation cites Rzepakowski et al. 2012.
I assume this is refering to Decision trees for uplift modeling with single and multiple treatments, but as far as I can tell that paper does not mention regularization anywhere.
Thanks!

[jeongyoonlee]

cc: @zhenyuz0500 @t-tte