This example demonstrates the WAI-ARIA support built into the RadDropDownTree.
Enable it by setting EnableAriaSupport="true" on the control. You can also provide a descriptive label for assistive technologies
using the AriaLabel property, which maps to the aria-label attribute on the rendered element.
The WAI-ARIA attributes allow screen readers and other assistive technologies to correctly announce the dropdown state (expanded/collapsed),
the tree structure, and the currently selected or focused node.