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 tags are not valid in HTML5. But currently browsers are supporting to parse them and also you can use them using css. So if you want to use custom tags for current browsers then you can. But the support may be taken away once the browsers implement W3C standards strictly for parsing the HTML content.