Under the hood, lepton-netlist consists of two parts and thus processes
schematic files in two steps. The first part called frontend
transforms all given schematics into an intermediate schematic model.
The second part called backend is a Scheme script that takes
that model and transforms its contents into a human readable output
using functions provided by lepton-netlist Scheme API. As you may now
guess, there are several backends in Lepton and each of them uses its
own way to transform the schematic model. In the command-line, the
user may specify only one backend at a time.