The element is empty or not fulfilling its content requirements.

# How do I fix this ?

Every element has a content model with requirements that need to be met. Make sure that you are using the element correctly and use a [reference](https://developer.mozilla.org/en-US/docs/Web/HTML/Element) if necessary.

# Resources

* [Content models](https://www.w3.org/TR/html5/dom.html#content-models)
* [Kinds of content](https://www.w3.org/TR/html5/dom.html#kinds-of-content)