* </ul>
 *
 * <h4>Example usage</h4>
 *
 * {@snippet :
 * class Foo {
 *   private static final ImmutableSet<String> RESERVED_CODES =
 *       ImmutableSet.of("AZ", "CQ", "ZX");
 *
 *   private final ImmutableSet<String> codes;
 *
 *   public Foo(Iterable<String> codes) {
 *     this.codes = ImmutableSet.copyOf(codes);

 * </ul>
 *
 * <h4>Example usage</h4>
 *
 * {@snippet :
 * class Foo {
 *   private static final ImmutableSet<String> RESERVED_CODES =
 *       ImmutableSet.of("AZ", "CQ", "ZX");
 *
 *   private final ImmutableSet<String> codes;
 *
 *   public Foo(Iterable<String> codes) {
 *     this.codes = ImmutableSet.copyOf(codes);

    /** Query parameter name for main search query. */
    public static final String OPTION_QUERY_Q = "q";

    /** Query parameter name for constraint query. */
    public static final String OPTION_QUERY_CQ = "cq";

    /** Query parameter name for optional query. */
    public static final String OPTION_QUERY_OQ = "oq";

    /** Query parameter name for negative query. */
    public static final String OPTION_QUERY_NQ = "nq";