code: func (b *builder) start() {
  	graphname := "unnamed"
  	if b.config.Title != "" {
  		graphname = b.config.Title
  	}
  	fmt.Fprintln(b, `digraph "`+graphname+`" {`)
  	fmt.Fprintln(b, `node [style=filled fillcolor="#f8f8f8"]`)
  }
docs: // start generates a title and initial node in DOT format.