/** The HTTP {@code If-None-Match} header field name. */
  public static final String IF_NONE_MATCH = "If-None-Match";
  /** The HTTP {@code If-Range} header field name. */
  public static final String IF_RANGE = "If-Range";
  /** The HTTP {@code If-Unmodified-Since} header field name. */
  public static final String IF_UNMODIFIED_SINCE = "If-Unmodified-Since";