@wilsonge :

1. Tab key: moves the focus to the first object in the tree view or moves the focus from the object in the tree view to the next object on the page.
2. About tabindex: See: 5.6.1 Managing Focus Within Components Using a Roving tabindex
3. aria-labelledby should refer to the ID of the header of this section

<div class="media-disk-name">Local</div>

This should be a headline, e.g. <h3 id="TreeViewPurposeID">Local</h3>
And then:

<ul class="media-tree" aria-labelledby="TreeViewPurposeID" ....>

Is this a sufficient explanation for you?

OK So @laoneo @dneukirchen I need some advice here. Unfortunately to make the tree work for the a11y requirements I need the drive to be part of the element list I think else things don't work. Is there any reason the drives can't be part of the list or in non-local adapters is there going to be cases where this is a bad idea?

@laoneo @dneukirchen bump

I need the drive to be part of the element list

What do you mean with that?

I am assuming that @wilsonge is referring to media-disk-name
I would probably add media-drive-name

They are currently disconnected from the list media-tree
They should be part of the tree

I need the drive to be part of the element list

I mean the media drive names (currently in the class media-drive-name) need to be part of the ul tree for a11y

I guess this needs some restructuring and some changes in tree and tree-item components, but i dont see a case where this should be a problem.
I can offer to test it with non local adapters once the changes are implemented.

Perfect. Thanks

OK So I've fixed the html structure. The tabindex stuff is implemented to the point of the active page item gets a tabindex of 0 and the rest -1. As I said I'm going to leave the keyboard navigation for someone else to take a stab at. @dneukirchen can you take a look as well to ensure the cloud plugins are still happy here

tested successfully.
it works (beside the fact that the dropbox plugin is out of date and was not autoloaded correctly)

html looks like

    <div class="media-sidebar col-md-2 d-none d-md-block">
        <div class="media-disk"><h2 id="disk-1" class="media-disk-name">Dropbox</h2>
            <div class="media-drive">
                <ul role="tree" aria-labelledby="disk-1" class="media-tree">
                    <li role="treeitem" aria-level="1" aria-setsize="0" aria-posinset="1" tabindex="0"
                        class="active media-tree-item media-drive-name"><a><span
                            class="item-name">Your Dropbox</span></a>
                        <ul role="group" class="media-tree">
                            <li role="treeitem" aria-level="2" aria-setsize="1" aria-posinset="0" tabindex="-1"
                                class="media-tree-item"><a><span class="item-icon"><span class="fa fa-folder-o"></span></span>
                                <span class="item-name">dwdwdw</span></a> <!----></li>
                        </ul>
                    </li>
                </ul>
            </div>
        </div>
        <div class="media-disk"><h2 id="disk-2" class="media-disk-name">Local</h2>
            <div class="media-drive">
                <ul role="tree" aria-labelledby="disk-2" class="media-tree">
                    <li role="treeitem" aria-level="1" aria-setsize="0" aria-posinset="1" tabindex="-1"
                        class="media-tree-item media-drive-name"><a><span class="item-name">images</span></a>
                        <ul role="group" class="media-tree">
                            <li role="treeitem" aria-level="2" aria-setsize="3" aria-posinset="0" tabindex="-1"
                                class="media-tree-item"><a><span class="item-icon"><span class="fa fa-folder-o"></span></span>
                                <span class="item-name">banners</span></a> <!----></li>
                            <li role="treeitem" aria-level="2" aria-setsize="3" aria-posinset="1" tabindex="-1"
                                class="media-tree-item"><a><span class="item-icon"><span class="fa fa-folder-o"></span></span>
                                <span class="item-name">headers</span></a> <!----></li>
                            <li role="treeitem" aria-level="2" aria-setsize="3" aria-posinset="2" tabindex="-1"
                                class="media-tree-item"><a><span class="item-icon"><span class="fa fa-folder-o"></span></span>
                                <span class="item-name">sampledata</span></a> <!----></li>
                        </ul>
                    </li>
                </ul>
            </div>
        </div>
    </div>

screenshot:

Looks like you have a lot of unnecessary aria attributes in there. I will check more closely later but you shouldnt need aria-setsize and aria-posint

https://developers.google.com/web/fundamentals/accessibility/semantics-aria/aria-labels-and-relationships#aria-posinset_aria-setsize

When the size of a set cannot be determined by the elements present in the DOM — such as when lazy rendering is used to avoid having all of a large list in the DOM at once — aria-setsize can specify the actual set size, and aria-posinset can specify the element's position in the set.

https://www.w3.org/TR/wai-aria-practices/examples/treeview/treeview-1/treeview-1b.html

I deliberately put them in because of the above link which says

The code in this example explicitly declares values for aria-setsize, aria-posinset and aria-level, which overrides browser computation of values for these properties. The ARIA 1.0 specification for these properties states that browsers can, but are not required to, compute these values.

Are you overriding the " browser computation of values for these properties."

https://www.w3.org/TR/wai-aria-practices/examples/treeview/treeview-1/treeview-1a.html

The ARIA 1.0 specification for these properties states that browsers can, but are not required to, compute their values. So, some browser and assistive technology combinations may not compute or report correct position and level information if it is not explicitly declared.

And i've struggled to find docs on what browsers do/don't support this. so seemed better safe than sorry

But no I'm not overriding anything

so seemed better safe than sorry

No problem I guess - @zwiastunsw will know better than me

Unfortunately, I don't know any better.
In my opinion, these attributes are not necessary. But their use will not cause confusion.
I asked for the opinion of an expert in ARIA. I should have received an answer in one day.

Its a bit old but reading through the post and examples it seems more up to date that the example you followed http://accessibleculture.org/articles/2013/02/not-so-simple-aria-tree-views-and-screen-readers/

I checked http://www.w3.org/TR/wai-aria-practices/examples/treeview/treeview-1/treeview-1a.html which does not use posinset etc and it works correctly in FF, Edge, Chrome on windows

The only reason that it might not work would be in a scenario where the entire tree is not in the dom at page load but was added dynamically on an event. That is not the case here.

I asked for the opinion of an expert in ARIA. I should have received an answer in one day.

Only after the holidays will I receive an answer.

@zwiastunsw Any updates from your contact. If we don't hear anything soon then I'd rather merge this in. I can start some work on the keyboard support and then we can easily come back and delete these extra attributes at a later point

Merging per above. More than happy to come back to this if/when we hear something back

1. The attributes posinset and setsize are not necessary. But they do not interfere. Chrome, FF, and NVDA work well without these attributes. But there may be other browsers that need these attributes.
2. The more important aria-expanded attribute is missing in the expanding branches
3. The <a> tags (without href attribute) are also unnecessary.