dom - What is HTML "is" attribute?

Question

I have seen it a lot here and there, yet I could find any description or documentation about it!

Example:

<paper-input-decorator label="Your Name">
    <input is="core-input">
</paper-input-decorator>

Answer 1

It is part of the W3C Draft spec for Web Components' Custom Elements.

Latest Working Draft: http://www.w3.org/TR/custom-elements/#type-extension-semantics

Latest Editor's Draft: http://w3c.github.io/webcomponents/spec/custom/#type-extension-example