Looking in the documentation for 'showline' parameter in 'update_figure'

I’m following the code example below. Unfortunately, right from the beginning I got stuck for hours. I didn’t see a difference between setting the ‘showline’ parameter to True and False but thought it was a good example to use for learning the documentation. I have not been able to find this described in the documentation though. Is it there? I have searched around for a long time.

# Go crazy styling the figure
fig.update_layout(
    # Shows gray line without grid, styling fonts, linewidths and more
    xaxis=dict(
        showline=True,
        showgrid=False,
        showticklabels=True,
        linecolor='rgb(204, 204, 204)',
        linewidth=2,
        ticks='outside',
        tickfont=dict(
            family='Arial',
            size=12,
            color='rgb(82, 82, 82)',
        ),
    ),
    # Turn off everything on y axis
    yaxis=dict(
        showgrid=False,
        zeroline=False,
        showline=False,
        showticklabels=False,
    ),
    autosize=False,
    margin=dict(
        autoexpand=False,
        l=100,
        r=20,
        t=110,
    ),
    showlegend=False,
    plot_bgcolor='white'
)

I did not find this in the docs, but I did find out that it is a line showing the axis in contrast to the plotting area.