[g-a-devel] HTML5 inert subtrees

[Alexander Surkov <surkov alexander gmail com>]

Hi.

HTML5 introduces inert subtrees [1] which are supposed to make a
portion of the document inactive (not interactive for the user):

"When a node or one of its ancestors is inert, then the user agent
must act as if the element was absent for the purposes of targeting
user interaction events, may ignore the node for the purposes of text
search user interfaces (commonly known as "find in page"), and may
prevent the user from selecting text in that node."

There is number of approaches discussed at w3c bugzilla [2]:

1. Map it to lack ATK_STATE_SENSITIVE (aria-disabled analogue applied
to any element)

I don't have data if this state is recognized by screen readers. In
Firefox it seems ENABLED and SENSITIVE states accompany each other if
the control doesn't have disabled state. So I'm not sure under what
circumstances ENABLED and SENSITIVE states are applied but probably
some combination of them would be a best match for inert subtrees.

2. Map it to aria-hidden.

aria-hidden implementation varies from browser to browser: Chrome
removes it from accessible tree, Firefox exposes "hidden" object
attribute. Having the same ambiguity in inert subtree implementation
seems unfortunate.

3. Remove from accessible tree approach (Chrome aria-hidden impl)

While it should work in most cases but it's not author error prone
approach and it doesn't 100% go with inert subtree description since
inert subtree may allow text selection (refer to "User agents should
allow the user to override the restrictions on search and text
selection, however."). Also screen magnifies or other AT might want to
"see" inert subtree, having no accessible prevents them from this.

4. Expose "hidden" object attribute on root (or every item from
subtree) of inert subtree (Firefox aria-hidden impl)

AT decides what it wants to do with it: either completely ignore it or
not. I'm not sure though if making the same mapping as aria-hidden is
a good choice.

5. Invent something new.

AT should support it and it takes a time but if nothing from existing
things suites well for inert subtrees then perhaps no other
alternatives.

I'd love to hear your thoughts.

Thank you.
Alexander.

[1] http://www.w3.org/html/wg/drafts/html/master/editing.html#inert-subtrees
[2] https://www.w3.org/Bugs/Public/show_bug.cgi?id=23350