If it had remained as the Irrelevant Attribute

I challenged the hidden attribute years ago because it seemed to me it was nothing more than an elemental equivalent of display: none. However, others, including the co-chairs, disagreed with me, and agreed with the HTML5 editor: the hidden attribute had the additional semantics related to its irrelevancy.

Based on this decision four years ago, I'm at a loss to understand why the HTML5 co-chairs would consider an option to allow aria-describedby to link to this content so that it can be rendered by screen readers—in effect, to make the content in the element with the hidden attribute, relevant. Something cannot be both relevant and irrelevant at the exact same time.

Read more in If it had remained the Irrelevant Attribute.