docs: function validate(cmd, args, info) {
    AbstractCommand.prototype.validate.apply(this, arguments);
    var index = parseInt(args[1])
      , value = info.db.getKey(args[0], info);
    if(value === undefined) {
      throw NoSuchKey;
    }else if(isNaN(index) || (index < 0 || index >= value.getLength())) {
      throw IndexRange;
    }
    args[1] = index;
  }