p-tree renders invalid html for accessibility

[Trakhan]

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Plunkr Case (Bug Reports)
No necessary.

Current behavior

Role of containing 'ul' element in tree DOM is overriden to role="tree" leaving child 'li' elements without parent with correct role.

<p-tree>
<div class="ui-tree ui-widget ui-widget-content ui-corner-all">
<ul class="ui-tree-container" role="tree">
<p-treenode>
<li class="ui-treenode ui-treenode-leaf" >
<div class="ui-treenode-content" role="treeitem" tabindex="0" draggable="false" aria-posinset="1" aria-selected="false">
<span class="ui-tree-toggler pi pi-fw ui-unselectable-text pi-caret-right"></span>
<span class="ui-treenode-label ui-corner-all" >
<span>Backup</span>
</span>
</div>
</li>
</p-treenode>
</ul>
</div>
</p-tree>

Found out with Axe chrome plugin (accessibility testing tool): https://www.deque.com/axe/

Expected behavior

Role of child elements should be probably overriden too. Simple solution could be moving role="treeitem" from div.ui-treenode-content to it's parent li element.

Minimal reproduction of the problem with instructions

What is the motivation / use case for changing the behavior?

Correct HTML accessibility tree;

Please tell us about your environment:

• Angular version: 7.2.6

• PrimeNG version: 7.0.5

• Browser: [all]

• Language: [all]