Targeting block 'section' tags specifically

Good afternoon all,

I'm trying to write a function related to accessibility, specifically adding an aria-label='whatever label is' attribute to 'section' tags on the site.

With the following, it applies to all blocks (div, nav, etc.). What I want (at least for now) is to target 'section' tags ONLY, but I can't for the life of me find how to target them specifically:

function mytheme_preprocess_block(&$variables) {
	$block = $variables['block'];  
        /* this adds the attribute, but many blocks do not have titles so it needs work */
	if (!empty($block->title)) {
		$variables['attributes_array']['aria-label'][] = $block->title;

	} else {
 		$variables['attributes_array']['aria-label'][] = 'This is a label';	
	}
}

Any help is greatly appreciated.