The rules are in https://eliben.github.io/lsystem/rules.js https://eliben.github.io/lsystem/rules.js and the evaluation is in https://eliben.github.io/lsystem/l

The rules are in https://eliben.github.io/lsystem/rules.js https://eliben.github.io/lsystem/rules.js and the evaluation is in https://eliben.github.io/lsystem/lsys.js https://eliben.github.io/lsystem/lsys.js It looks like f and g are special rules for moving with the pen down or the pen up.