Are custom elements valid HTML5?

Question

I\'ve been unable to find a definitive answer to whether custom tags are valid in HTML5, like this:

Hello!

Answer 1

Custom HTML elements are an emerging W3 standard I have been contributing to that enables you to declare and register custom elements with the parser, you can read the spec here: W3 Web Components Custom Elements spec. Additionally, Microsoft supports a library (written by former Mozilla devs), called X-Tag - it makes working with Web Components even easier.