The question remaining is: Which level of offline mode will we support? It
  seems reasonable to assume that users will be able to tell when localhost is
  not active (in most cases, localhost should be available, even if the rest of
  the network is not). Therefore, let's concentrate on the state where no
  network <beyond localhost> exists, and leave the more extreme state to users
  to diagnose and correct as necessary.

* Why is Offline Mode Important?

        assertTrue(DefaultMirrorSelector.matchPattern(getRepo("a", "http://localhost"), "*"));
        assertFalse(DefaultMirrorSelector.matchPattern(getRepo("a", "http://localhost"), "external:*"));

        assertTrue(DefaultMirrorSelector.matchPattern(getRepo("a", "http://localhost"), "external:*,a"));
        assertFalse(DefaultMirrorSelector.matchPattern(getRepo("a", "http://localhost"), "external:*,!a"));

     * <ul>
     * <li>{@code *} (since 2.0.5)= everything,</li>
     * <li>{@code external:*}  (since 2.0.9)= everything not on the localhost and not file based,</li>
     * <li>{@code external:http:*} (since 3.8.0)= any repository not on the localhost using HTTP,</li>
     * <li>{@code repo,repo1}  (since 2.0.9)= {@code repo} or {@code repo1},</li>