💡 add some comments

lib/src/enums/duplicates.dart

@@ -1,3 +1,4 @@
+/// An enum of all available duplicate handling strategies.
 enum Duplicates {
   combine,
   first,

lib/src/enums/format.dart

@@ -1,5 +1,6 @@
 typedef Formatter = String Function(String value);
 
+/// An enum of all supported URI component encoding formats.
 enum Format {
   rfc1738(_rfc1738Formatter),
 

lib/src/enums/list_format.dart

@@ -1,5 +1,6 @@
 typedef ListFormatGenerator = String Function(String prefix, [String? key]);
 
+/// An enum of all available list format options.
 enum ListFormat {
   brackets(_brackets),
   comma(_comma),

lib/src/enums/sentinel.dart

@@ -1,3 +1,4 @@
+/// An enum of all available sentinels.
 enum Sentinel {
   /// This is what browsers will submit when the ✓ character occurs in an
   /// application/x-www-form-urlencoded body and the encoding of the page containing

lib/src/extensions/extensions.dart

@@ -1,9 +1,11 @@
 import 'package:qs_dart/src/models/undefined.dart';
 
 extension IterableExtension<T> on Iterable<T> {
+  /// Returns a new [Iterable] without [Undefined] elements.
   Iterable<T> whereNotUndefined() => where((T el) => el is! Undefined);
 }
 
 extension ListExtension<T> on List<T> {
+  /// Returns a new [List] without [Undefined] elements.
   List<T> whereNotUndefined() => where((T el) => el is! Undefined).toList();
 }