use document#qsa to traverse the dom

lib/single-file/util/doc-helper.js

@@ -160,10 +160,9 @@ this.docHelper = this.docHelper || (() => {
 		return removeQuotes(fontFamilyName.trim()).toLowerCase();
 	}
 
-	function getElementsInfo(win, element, elementsInfo = new Map()) {
-		const elements = Array.from(element.childNodes).filter(node => node.nodeType == 1);
-		elements.forEach(element => {
-			getElementsInfo(win, element, elementsInfo);
+	function getElementsInfo(win, element) {
+		const elementsInfo = new Map();
+		element.querySelectorAll("*").forEach(element => {
 			setInfo(win, element, elementsInfo);
 			setInfo(win, element, elementsInfo, ":first-letter");
 			setInfo(win, element, elementsInfo, ":before");