[Shadow DOM] Make Shadow DOM optional

[Nevraeka]

It has been argued that HTML Imports, Templates, & Shadow DOM are add ons for Custom Elements. The Polymer library will always use Shadow DOM (polyfilled or native). It would be a great advantage to have Shadow DOM as a configuration flag globally in the flags object OR even at the element level with a property like shadow : false.

Any thoughts on this?

[ebidel]

I think we're exploring this for 0.8 and beyond. @sorvell and @sjmiles will have more info.

[ssorallen]

Disabling shadow DOM completely would affect the common practice of using id attributes for element references and for styling. If an element is used more than once on a page, wouldn't the page have multiple elements with the same ID?

[Nevraeka]

Yes It would. I would do this only per element

[justinfagnani]

This is configurable now. See https://github.com/Polymer/polymer/blob/0.8-preview/PRIMER.md#global-polymer-settings