When lists of links are displayed on a page for navigational purpose, it can become difficult for users utilizing assistive technologies to navigate between these lists while maintaining an understanding of the purpose of the links. The <ul> element also does not convey proper context.
Starting in WordPress 5.5, a new theme support feature (navigation-widgets) has been added to address this issue. When support is declared, all default widgets included in WordPress Core that produce lists of links will be output wrapped in the <nav> element. Note: the markup produced inside this wrapper will remain unchanged.
Additionally, an arial-label attribute (which is
