mostly finished rewrite

public/node_modules/dom-helpers/esm/contains.js

@@ -0,0 +1,14 @@
+/* eslint-disable no-bitwise, no-cond-assign */
+
+/**
+ * Checks if an element contains another given element.
+ * 
+ * @param context the context element
+ * @param node the element to check
+ */
+export default function contains(context, node) {
+  // HTML DOM and SVG DOM may have different support levels,
+  // so we need to check on context instead of a document root element.
+  if (context.contains) return context.contains(node);
+  if (context.compareDocumentPosition) return context === node || !!(context.compareDocumentPosition(node) & 16);
+}