def set_frame(ax):
    """Example of setting the frame of the plot box.
    """
    ax.spines['top'].set_visible(False)
    ax.spines['right'].set_visible(False)
    ax.spines['bottom'].set_visible(True)
    ax.spines['left'].set_visible(True)
    ax.xaxis.set_ticks_position('bottom')
    ax.yaxis.set_ticks_position('left')
    ax.get_xaxis().set_tick_params(direction='out')
    ax.get_yaxis().set_tick_params(direction='out')
    return ax
