enable positioning of horizontal legend below xaxis label

I want to put a (long) legend horizontally and below the xaxis.

But I have some trouble with positioning.

1. By default, the legend runs into the axis label (see Fig. below).
2. Putting the legend below the xaxis seems to require some guessing for a negative y (or are the better ways?

Plotly.newPlot('graph', [
   {  y: [2, 1, 3]},
   {  y: [4, 2, 5]},
   {  y: [3, 3, 6]},
  ],
  {xaxis: {title: {text: 'axis label'}},
           legend: {title: {text: 'legend title'},
                    orientation: 'h'}
  }
)

https://jsfiddle.net/5udmbkza

从提供的 JSFiddle 开始，使用 issue 中的 Plotly.newPlot 配置，在 x 轴标签下方复现水平图例。跟踪图例和轴标签在布局中的定位方式，然后验证长水平图例可以放置在 x 轴下方，而不会发生重叠，也不需要手动猜测负 y 值。