* <pre>{@code
   * static final ImmutableGraph<Country> COUNTRY_ADJACENCY_GRAPH =
   *     GraphBuilder.undirected()
   *         .<Country>immutable()
   *         .putEdge(FRANCE, GERMANY)
   *         .putEdge(FRANCE, BELGIUM)
   *         .putEdge(GERMANY, BELGIUM)
   *         .addNode(ICELAND)
   *         .build();
   * }</pre>
   *
   * <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build

    HEX_22(
        CharMatcher.inRange('0', '9')
            .or(CharMatcher.inRange('A', 'F'))
            .or(CharMatcher.inRange('a', 'f')),
        "0123456789ABCDEFabcdef"),
    GERMAN_59(
        CharMatcher.inRange('a', 'z')
            .or(CharMatcher.inRange('A', 'Z'))
            .or(CharMatcher.anyOf("äöüßÄÖÜ")),
        "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZäöüßÄÖÜ");

    HEX_22(
        CharMatcher.inRange('0', '9')
            .or(CharMatcher.inRange('A', 'F'))
            .or(CharMatcher.inRange('a', 'f')),
        "0123456789ABCDEFabcdef"),
    GERMAN_59(
        CharMatcher.inRange('a', 'z')
            .or(CharMatcher.inRange('A', 'Z'))
            .or(CharMatcher.anyOf("äöüßÄÖÜ")),
        "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZäöüßÄÖÜ");