Unfortunately it is not technically possible to polyfill all Web Components APIs. Shadow DOM is especially hard to polyfill in any sensible way (Google did try

Unfortunately it is not technically possible to polyfill all Web Components APIs. Shadow DOM is especially hard to polyfill in any sensible way (Google did try it, but failed to deliver a solution that would cover all use cases). I'm sorry for the missing documentation on Github, I will write a proper project description with some examples later next week.