ref!: use default parameters to break compatibility with older browsers

ajquery.js

@@ -1,7 +1,7 @@
-function $(sel, el) {
-  return (el || document).querySelector(sel);
+function $(sel, $parent = document) {
+  return $parent.querySelector(sel);
 }
 
-function $$(sel, el) {
-  return Array.from((el || document).querySelectorAll(sel));
+function $$(sel, $parent = document) {
+  return Array.from($parent.querySelectorAll(sel));
 }