绘制流程图，形成文档
可以使用的工具 https://www.websequencediagrams.com/ MY CHOICE: https://mermaidjs.github.io/ Another choice: google key word: sequence graph 把 svg 转换成 png 文件 Or without installing anything:
It will produce picture.svg.png that is 1000 pixels wide.
I have tested it only on OS X 10.6.3.
例如： ……