The points on the x-axis for which there are markers and grid lines.

        There are default ticks, but you can pass values to this method to
        override the defaults. Otherwise the method will return the ticks.

        :param \*ticks: if given, these will be chart's x-ticks.
        :rtype: ``tuple``

def x_ticks(self, *ticks):
        """The points on the x-axis for which there are markers and grid lines.

        There are default ticks, but you can pass values to this method to
        override the defaults. Otherwise the method will return the ticks.

        :param \*ticks: if given, these will be chart's x-ticks.
        :rtype: ``tuple``"""

        if ticks:
            for tick in ticks:
                if not is_numeric(tick):
                    raise TypeError("'%s' is not a numeric tick" % str(tick))
            self._x_ticks = tuple(sorted(ticks))
        else:
            if self._x_ticks:
                return self._x_ticks
            else:
                return determine_ticks(self.x_lower_limit(), self.x_upper_limit())