===== Useful links =====
  * https://developer.mozilla.org/zh-CN/docs/Learn/JavaScript/First_steps/What_is_JavaScript
  * https://www.zhihu.com/question/19913979
  * http://nglviewer.org/ngl/gallery/  (try 6ND6 ribosome, 5ZAL Dicer and 3JB9 spliceosome）