2.2.28 [W3C-HTML52] Section 5.1. The hidden attribute
C0070: Assistive technologies determine what is done with the hidden items
The specification states:
... The hidden attribute ... When such features are available, User Agents may use them to expose the full semantics of hidden elements to AT when appropriate, if such content is referenced indirectly by an ID reference or valid hash-name reference. This allows ATs to access the structure of these hidden elements upon user request, while keeping the content hidden in all presentations of the normal document flow. Authors who wish to prevent user-initiated viewing of a hidden element should not reference the element with such a mechanism.
Assistive technologies have access to elements that are in the hidden state, and those technologies determine what is done with the hidden items.