/** Path separator (":" on UNIX). */
  PATH_SEPARATOR("path.separator"),

  /** Line separator ("\n" on UNIX). */
  LINE_SEPARATOR("line.separator"),

  /** User's account name. */
  USER_NAME("user.name"),

  /** User's home directory. */
  USER_HOME("user.home"),

  /** User's current working directory. */
  USER_DIR("user.dir");

  private final String key;