code: func (mod *Module) Copy() *Module {
  	cpy := *mod
  	cpy.Rules = make([]*Rule, len(mod.Rules))
  	for i := range mod.Rules {
  		cpy.Rules[i] = mod.Rules[i].Copy()
  	}
  	cpy.Imports = make([]*Import, len(mod.Imports))
  	for i := range mod.Imports {
  		cpy.Imports[i] = mod.Imports[i].Copy()
  	}
  	cpy.Package = mod.Package.Copy()
  	return &cpy
  }
docs: // Copy returns a deep copy of mod.