Add the content of the package.

lib/src/all.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import '../boolean_selector.dart';
+
+/// A selector that matches all inputs.
+class All implements BooleanSelector {
+  final variables = const [];
+
+  const All();
+
+  bool evaluate(semantics) => true;
+
+  BooleanSelector intersection(BooleanSelector other) => other;
+
+  BooleanSelector union(BooleanSelector other) => this;
+
+  void validate(bool isDefined(String variable)) {}
+
+  String toString() => "<all>";
+}