code: func (f *SourceFile) WriteHeader(title, pack string, imports []*ImportSpec) error {
  	ctx := map[string]interface{}{
  		"Title":       title,
  		"ToolVersion": version.String(),
  		"Pkg":         pack,
  		"Imports":     imports,
  	}
  	if err := headerTmpl.Execute(f, ctx); err != nil {
  		return fmt.Errorf("failed to generate contexts: %s", err)
  	}
  	return nil
  }
docs: // WriteHeader writes the generic generated code header.