it's part of Chrome Lighthouse test, but this is separated

lighthouseDomTest.js

'use strict';

function lighthouseDomTest ( /** @type {Element} */ rootElement )
{
	let maxDepth = 0;
	let maxDepthElement = null;
	let mostChildren = 0;
	let mostChildrenElement = null;
	let allElements = rootElement.querySelectorAll( '*' );
	allElements.forEach( ( element ) =>
	{
		let currentElement = element;
		if ( !currentElement.children.length ) {
			let steps = 0;
			while ( currentElement !== rootElement ) {
				steps++;
				currentElement = currentElement.parentElement;
			}
			if ( maxDepth < steps ) {
				maxDepth = steps;
				maxDepthElement = element;
			}
		}
		if ( element.children.length > mostChildren ) {
			mostChildren = element.children.length;
			mostChildrenElement = element;
		}
	} );
	return {
		'totalElementNodes': allElements.length,
		'maxDepth': maxDepth,
		'maxDepthElement': maxDepthElement,
		'mostChildren': mostChildren,
		'mostChildrenInElement': mostChildrenElement,
	};
}

lighthouseDomTest( document.body );

https://developers.google.com/web/tools/lighthouse/audits/dom-size