Can a label only refer to input elements?

Question

W3Schools have this to say about labels:

The tag defines a label for an input element. _{[Emphasis mine]<}

Answer 1

The latest WhatWG spec has this to say:

Some elements, not all of them form-associated, are categorized as labelable elements. These are elements that can be associated with a label element.

• button, input (if the type attribute is not in the Hidden state), meter, output, progress, select, textarea

...

The for attribute may be specified to indicate a form control with which the caption is to be associated. If the attribute is specified, the attribute's value must be the ID of a labelable element in the same tree as the label element.

(Source: https://html.spec.whatwg.org/multipage/forms.html.)

In other words, the standard only allows for attributes to point at elements of one of the 7 tag types listed above. The HTML exhibited in the question (which uses a for element to point to an editable div) is therefore technically invalid HTML under the current spec.

The Nu Html Checker (which is endorsed by WhatWG) agrees; if you ask it to validate the HTML document from the question, it will say:

Error: The value of the for attribute of the label element must be the ID of a non-hidden form control.