Proposal for changes to manage Shadow DOM content distribution

Summary

This document considers real-world usage of Shadow DOM in three large production component libraries, and identifies a number of issues with the current Shadow DOM design. This document proposes to address those issues by updating the Shadow DOM spec to:

1. Allow elements to identify insertion points by name rather than a CSS selector.
2. Support standard subclassing semantics by which a subclass can populate a named base class’ insertion point, and optionally expose an insertion point with the same name.

Significantly, these changes are compatible with the notion of supporting a maximum of one shadow root per element.

This document is not intended to be a complete, final proposal for a spec change. Rather, it is intended primarily to stimulate discussion at the Web Components Face-to-Face meeting on April 24, 2015.