The component model effort brings encapsulation to the Web. See ​use cases for more background.

Implementation Status

_{If this is older than 30 days, it's probably out of date.}

At this point, no author-facing APIs are exposed.

Differences and similarities with ​XBL2:

Area	Status	Differences
Events	Matches logic in ​event handlers section	We don't create a separate Event object for each re-targeting, because we don't worry about component isolation (yet)
Shadow Root	We now create a root object at which the shadow DOM subtree begins	Instead of it being a <template> element clone, we use a different node type (SHADOW_ROOT_NODE = 14)
pseudo attribute	Same as ​XBL2 pseudo	Allows arbitrary value and CSS machinery has been modified to allow any value
CSS matching	Some of the ​selectors and shadow scopes implemented	Need to further align with the XBL2 spec
Tree Scopes	Implemented, matches the ​shadow scope notion of in XBL2
Style blocks/script blocks	Not yet implemented
Inheritance	Won't be implementing	We decided that this feature is overly complex and unnecessary for the component model. See ​this post to public-webapps
<content> element	Basic building blocks are being used by <summary> and <details>	Need to better understand requirements and use cases to spec/implement properly. Certainly won't be implementing the way it's ​defined in XBL 2.0