Shadow DOM is designed to provide encapsulation by hiding DOM subtrees under shadow roots. It provides a method of establishing and maintaining functional boundaries between DOM trees and how these trees interact with each other within a document, thus enabling better functional encapsulation within the DOM.

What the Heck is Shadow DOM?
http://glazkov.com/2011/01/14/what-the-heck-is-shadow-dom/

Web Components Explained - Shadow DOM
https://dvcs.w3.org/hg/webcomponents/raw-file/57f8cfc4a7dc/explainer/index.html#shadow-dom-section

HTML5Rocks - Shadow DOM 101
http://www.html5rocks.com/en/tutorials/webcomponents/shadowdom/

HTML5Rocks - Shadow DOM 201: CSS and Styling
http://www.html5rocks.com/en/tutorials/webcomponents/shadowdom-201/

HTML5Rocks - Shadow DOM 301: Advanced Concepts & DOM APIs
http://www.html5rocks.com/en/tutorials/webcomponents/shadowdom-301/