https://custom-elements-everywhere.com/
https://github.com/webcomponents/custom-elements-everywhere
https://developers.google.com/web/fundamentals/web-components/customelements

https://learn.javascript.ru/webcomponent-core

2018
https://blog.sessionstack.com/how-javascript-works-under-the-hood-of-custom-elements-best-practices-on-building-reusable-e118e888de0c
    https://habr.com/company/ruvds/blog/419831/