Is your feature request related to a problem? Please describe.
Problem is that some content of viewers need encapsulation to incorporate own styles and scripts, like HTML generated from TEI in TextView.

Describe the solution you'd like
Simple encapsulation of DOM-related features. Easy solution is a web component that induces a shadowDOM in which contents are held.

Describe alternatives you've considered
Script to move contents into newly created shadowDOM dynamically, as inline code.

Additional context
In conjunction with https://github.com/Edirom/Edirom-Online-Backend/tree/ftr-133-add-support-for-tei-rendition this resolves Edirom/Edirom-Online-Backend#135