The desciption is coming soon. Basically, the method was fully described in our article published in Journal of Coputer-Aided Molecular Design: Zhonghua Xia, Pavel Karpov, Grzegorz Popowicz and Igor V. Tetko. Focused Library Generator: case of Mdmx inhibitors.
The source code is available on https://github.com/bigchem/online-chem