正则
- https://billie66.github.io/TLCL/book/chap20.html
- https://www.regular-expressions.info/dot.html
- https://www.phpliveregex.com/
- https://www.debuggex.com/
- https://deerchao.cn/tutorials/regex/regex.htm
- https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Guide/Regular_Expressions
- http://www.pyregex.com/
- https://jex.im/regulex/#!flags=&re=%5E(a%7Cb)*%3F%24