Move internal modules to “internal” folder.

.internal/insertWrapDetails.js

@@ -0,0 +1,23 @@
+/** Used to match wrap detail comments. */
+const reWrapComment = /\{(?:\n\/\* \[wrapped with .+\] \*\/)?\n?/;
+
+/**
+ * Inserts wrapper `details` in a comment at the top of the `source` body.
+ *
+ * @private
+ * @param {string} source The source to modify.
+ * @returns {Array} details The details to insert.
+ * @returns {string} Returns the modified source.
+ */
+function insertWrapDetails(source, details) {
+  const length = details.length;
+  if (!length) {
+    return source;
+  }
+  const lastIndex = length - 1;
+  details[lastIndex] = (length > 1 ? '& ' : '') + details[lastIndex];
+  details = details.join(length > 2 ? ', ' : ' ');
+  return source.replace(reWrapComment, `{\n/* [wrapped with ${ details }] */\n`);
+}
+
+export default insertWrapDetails;