Based on the current W3 Web Components draft, X-Tag enables the custom element portion of the proposal. Custom elements let you register new tags/elements with the parser so they are recognized and inflated with special abilities you define.
Find out more about what X-Tag does, where it works, and how to use it, on the project page here: http://mozilla.github.com/x-tag/
X-Tag (excluding third-party icons or images) is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
To get started hacking on X-Tag, first check out the code here:
git clone https://github.com/mozilla/x-tag
If you're interested in exploring the tags we've already created, check out our x-tag-elements repository.
git clone --recursive https://github.com/mozilla/x-tag-elements
To get started making your own X-Tags visit x-tags.org.
Share your tags by adding them to the offical X-Tag Registry.