The HTML attribute ##aria-hidden="true"## should be whitelisted in https://phabricator.wikimedia.org/source/mediawiki/browse/master/includes/parser/Sanitizer.php$832 around line 832.
The effect is supposed to be rather similar to ##role="presentation"## but the semantics are slightly different.
Elements which are repeating information already available but confusing for blind people shall be suppressed entirely.
A typical case is an eye-catching icon. That might be sufficient to explain the functionality completely for those who can see it, and such readers might ignore the textual description nearby. When listening the screenreader the icon will be mentioned and explained by name, but that does not tell anything. Such elements shall be omitted, focussing now on the remaining textual instructions. However, it is not always a presentational role.
While ##role="presentation"## is intended for decorative elements, like images and lines, ##aria-hidden="true"## shall suppress less important annotations, amendments, notes, which are confusing and related by optical position but not joined to what they shall extend, perhaps a joke or quote.
This is a follow-up of T26659.