It is fine to use hidden to hide tabpanels. The spec needs a correction.

[ianthedev]

The spec of the hidden attribute says the attribute shouldn't be used to hide tabpanels:

The hidden attribute must not be used to hide content that could legitimately be shown in another presentation. For example, it is incorrect to use hidden to hide panels in a tabbed dialog, because the tabbed interface is merely a kind of overflow presentation — one could equally well just show all the form controls in one big page with a scrollbar. It is similarly incorrect to use this attribute to hide content just from one presentation — if something is marked hidden, it is hidden from all presentations, including, for instance, screen readers.

But the WAI-ARIA's official demos of the tabs widget use the attribute to hide tabpanels. I had a discussion with an accessibility expert about this issue and was informed that the spec is wrong.

[domenic]

Dupe of #4904. The spec is not wrong, but it could be clearer.

[domenic]

#4904 (comment) is a good summary, in particular.