What is a labelable element?

Question

I have been reading on accessibility and a concept I cannot find accurate information on stumbled upon me: HTML labelable elements.

I understand that the concept behind a labelable element is one that can be properly wrapped or referenced by a <label>, for example:

<label>
    Enter some data
    <input type="text"/>
</label>

Or for example:

<label for="anInputField">
    Enter some data
</label>

<input type="text" id="anInputField"/>

Does anyone know exactly what labeable HTML elements are and which are not?

Bonus Round! Can you elaborate on why the fifth rule of ARIA use is a work in progress? In my own websites, I would like to be able to account for future changes to that, but I don't know why it's not set in stone (seems like it should be).

Answer 1

According to MDN, the following elements are labelable.

Excerpt from Content categories:

labelable Elements that can be associated with elements. Contains <button>, <input>, <keygen>, <meter>, <output>, <progress>, <select>, and <textarea>.

Answer 2

The link in the current HTML 5 recommendation (unlike the one to the HTML 5.1 draft in the ARIA draft you link to) isn't broken. It says:

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) keygen meter output progress select textarea