Add the content of the package.

lib/src/intersection_selector.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';
+import 'union_selector.dart';
+
+/// A selector that matches inputs that both of its sub-selectors match.
+class IntersectionSelector implements BooleanSelector {
+  final BooleanSelector _selector1;
+  final BooleanSelector _selector2;
+
+  Iterable<String> get variables sync* {
+    yield* _selector1.variables;
+    yield* _selector2.variables;
+  }
+
+  IntersectionSelector(this._selector1, this._selector2);
+
+  bool evaluate(semantics) =>
+      _selector1.evaluate(semantics) && _selector2.evaluate(semantics);
+
+  BooleanSelector intersection(BooleanSelector other) =>
+      new IntersectionSelector(this, other);
+
+  BooleanSelector union(BooleanSelector other) =>
+      new UnionSelector(this, other);
+
+  void validate(bool isDefined(String variable)) {
+    _selector1.validate(isDefined);
+    _selector2.validate(isDefined);
+  }
+
+  String toString() => "($_selector1) && ($_selector2)";
+}